Hello,
I just installed a new/clean version of Sage 8.6.0.
I ran npm install as per the docs and this failed.
Tried installing with both Node v9.11.2, NPM 5.6.0 and Node v8.17.0, NPM 6.13.4.
Same result each time 
Here’s the relevant log output:
olivermcvey@Olivers-iMac-Pro ~ % cd /Volumes/Macintosh\ HD/Users/olivermcvey/Local\ Sites/sage/app/public/wp-content/themes/sage-8.6.0
olivermcvey@Olivers-iMac-Pro sage-8.6.0 % npm install
npm WARN deprecated gulp-util@3.0.8: gulp-util is deprecated - replace it, following the guidelines at https://medium.com/gulpjs/gulp-util-ca3b1f9f9ac5
npm WARN deprecated chokidar@2.1.8: Chokidar 2 will break on node v14+. Upgrade to chokidar 3 with 15x less dependencies.
npm WARN deprecated browserslist@1.7.7: Browserslist 2 could fail on reading Browserslist >3.0 config used in other tools.
npm WARN deprecated request@2.88.2: request has been deprecated, see https://github.com/request/request/issues/3142
npm WARN deprecated fsevents@1.2.13: fsevents 1 will break on node v14+ and could be using insecure binaries. Upgrade to fsevents 2.
npm WARN deprecated svgo@0.7.2: This SVGO version is no longer supported. Upgrade to v2.x.x.
npm WARN deprecated har-validator@5.1.5: this library is no longer supported
npm WARN deprecated resolve-url@0.2.1: https://github.com/lydell/resolve-url#deprecated
WARN registry Unexpected warning for https://registry.npmjs.org/: Miscellaneous Warning EINTEGRITY: sha1-g0D8RwLDEi310iKI+IKD9RPT/dQ= integrity checksum failed when using sha1: wanted sha1-g0D8RwLDEi310iKI+IKD9RPT/dQ= but got sha512-Kb3PrPYz4HanVF1LVGuAdW6LoVgIwjUYJGzFe7NDrBLCN4lsV/5J0MFurV+ygS4bRVwrCEt2c7MQ1R2a72oJDw==. (4249 bytes)
WARN registry Using stale package data from https://registry.npmjs.org/ due to a request error during revalidation.
> fsevents@1.2.13 install /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/glob-watcher/node_modules/fsevents
> node install.js
gyp ERR! configure error
gyp ERR! stack Error: Can't find Python executable "python", you can set the PYTHON env variable.
gyp ERR! stack at PythonFinder.failNoPython (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:483:19)
gyp ERR! stack at PythonFinder.<anonymous> (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:397:16)
gyp ERR! stack at F (/usr/local/lib/node_modules/npm/node_modules/which/which.js:68:16)
gyp ERR! stack at E (/usr/local/lib/node_modules/npm/node_modules/which/which.js:80:29)
gyp ERR! stack at /usr/local/lib/node_modules/npm/node_modules/which/which.js:89:16
gyp ERR! stack at /usr/local/lib/node_modules/npm/node_modules/which/node_modules/isexe/index.js:42:5
gyp ERR! stack at /usr/local/lib/node_modules/npm/node_modules/which/node_modules/isexe/mode.js:8:5
gyp ERR! stack at FSReqWrap.oncomplete (fs.js:170:21)
gyp ERR! System Darwin 21.5.0
gyp ERR! command "/usr/local/bin/node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
gyp ERR! cwd /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/glob-watcher/node_modules/fsevents
gyp ERR! node -v v9.11.2
gyp ERR! node-gyp -v v3.6.2
gyp ERR! not ok
> node-sass@3.13.1 install /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-sass
> node scripts/install.js
Downloading binary from https://github.com/sass/node-sass/releases/download/v3.13.1/darwin-x64-59_binding.node
Cannot download "https://github.com/sass/node-sass/releases/download/v3.13.1/darwin-x64-59_binding.node":
HTTP error 404 Not Found
Hint: If github.com is not accessible in your location
try setting a proxy via HTTP_PROXY, e.g.
export HTTP_PROXY=http://example.com:1234
or configure npm proxy via
npm config set proxy http://example.com:8080
> es5-ext@0.10.61 postinstall /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/es5-ext
> node -e "try{require('./_postinstall')}catch(e){}" || exit 0
> node-sass@3.13.1 postinstall /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-sass
> node scripts/build.js
Building: /usr/local/bin/node /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-gyp/bin/node-gyp.js rebuild --verbose --libsass_ext= --libsass_cflags= --libsass_ldflags= --libsass_library=
gyp info it worked if it ends with ok
gyp verb cli [ '/usr/local/bin/node',
gyp verb cli '/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-gyp/bin/node-gyp.js',
gyp verb cli 'rebuild',
gyp verb cli '--verbose',
gyp verb cli '--libsass_ext=',
gyp verb cli '--libsass_cflags=',
gyp verb cli '--libsass_ldflags=',
gyp verb cli '--libsass_library=' ]
gyp info using node-gyp@3.8.0
gyp info using node@9.11.2 | darwin | x64
gyp verb command rebuild []
gyp verb command clean []
gyp verb clean removing "build" directory
gyp verb command configure []
gyp verb check python checking for Python executable "python2" in the PATH
gyp verb `which` failed Error: not found: python2
gyp verb `which` failed at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)
gyp verb `which` failed at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)
gyp verb `which` failed at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5
gyp verb `which` failed at FSReqWrap.oncomplete (fs.js:170:21)
gyp verb `which` failed python2 { Error: not found: python2
gyp verb `which` failed at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)
gyp verb `which` failed at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)
gyp verb `which` failed at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5
gyp verb `which` failed at FSReqWrap.oncomplete (fs.js:170:21)
gyp verb `which` failed stack: 'Error: not found: python2\n at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)\n at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)\n at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5\n at FSReqWrap.oncomplete (fs.js:170:21)',
gyp verb `which` failed code: 'ENOENT' }
gyp verb check python checking for Python executable "python" in the PATH
gyp verb `which` failed Error: not found: python
gyp verb `which` failed at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)
gyp verb `which` failed at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)
gyp verb `which` failed at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5
gyp verb `which` failed at FSReqWrap.oncomplete (fs.js:170:21)
gyp verb `which` failed python { Error: not found: python
gyp verb `which` failed at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)
gyp verb `which` failed at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)
gyp verb `which` failed at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5
gyp verb `which` failed at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5
gyp verb `which` failed at FSReqWrap.oncomplete (fs.js:170:21)
gyp verb `which` failed stack: 'Error: not found: python\n at getNotFoundError (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:13:12)\n at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:19)\n at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5\n at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5\n at FSReqWrap.oncomplete (fs.js:170:21)',
gyp verb `which` failed code: 'ENOENT' }
gyp ERR! configure error
gyp ERR! stack Error: Can't find Python executable "python", you can set the PYTHON env variable.
gyp ERR! stack at PythonFinder.failNoPython (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-gyp/lib/configure.js:484:19)
gyp ERR! stack at PythonFinder.<anonymous> (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-gyp/lib/configure.js:406:16)
gyp ERR! stack at F (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:68:16)
gyp ERR! stack at E (/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:80:29)
gyp ERR! stack at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/which/which.js:89:16
gyp ERR! stack at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/index.js:42:5
gyp ERR! stack at /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/isexe/mode.js:8:5
gyp ERR! stack at FSReqWrap.oncomplete (fs.js:170:21)
gyp ERR! System Darwin 21.5.0
gyp ERR! command "/usr/local/bin/node" "/Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-gyp/bin/node-gyp.js" "rebuild" "--verbose" "--libsass_ext=" "--libsass_cflags=" "--libsass_ldflags=" "--libsass_library="
gyp ERR! cwd /Users/olivermcvey/Local Sites/sage/app/public/wp-content/themes/sage-8.6.0/node_modules/node-sass
gyp ERR! node -v v9.11.2
gyp ERR! node-gyp -v v3.8.0
gyp ERR! not ok
Build failed with error code: 1
npm WARN ws@8.2.3 requires a peer of bufferutil@^4.0.1 but none is installed. You must install peer dependencies yourself.
npm WARN ws@8.2.3 requires a peer of utf-8-validate@^5.0.2 but none is installed. You must install peer dependencies yourself.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! node-sass@3.13.1 postinstall: `node scripts/build.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the node-sass@3.13.1 postinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! /Users/olivermcvey/.npm/_logs/2022-06-09T18_47_54_334Z-debug.log