Matt’s issue here: Aborted trying to redefine constant 'MULTISITE'. `define('MULTISITE', ...)` has already been occurred elsewhere - was also a problem for me. The replies obviously weren’t very helpful.
The solution for me was to ignore most of this documentation: https://roots.io/trellis/docs/multisite/ – as it appears to be outdated.
So, in other words, don’t add anything to your applications.php file. Also, the /wp/ directory issues seem to be resolved and can be ignored. Defining the “domain_current_site: store1.example.com” in your .yml seems to also not be necessary.
Updating the wordpress_sites.yml with the correct values seemed to be the only thing that actually had to be done now. WITH THE EXCEPTION of me having to still leave “Config::define(‘SUBDOMAIN_INSTALL’, true);” in the applications.php file – in order to actually get my subdomains working (even though I defined them as “true” in wordpress_sites.yml – not sure why I still had to do that, but that did indeed get me up and running).
What Matt mentioned in his post was also happening to me on deploys.
Hope this helps someone.