Notice: Array to string conversion in /var/www/app/web/wp/wp-includes/general-template.php on line 1200

[strarsis]

Btw. for Sage 9 there is an update branch in progress that fixes a lot of problems, notably with the webpack build:

Sage "9.1": Please test

This is primarily meant for updating existing Sage 9 themes so they build again properly (newer node and npm versions). Updating should be easy as most what is changed consists of “glue” code. Then there are some devs that have familiarized with Sage 9 and are still learning Sage 10 (notably the webpack and acorn part), hence they will still start new theme projects with Sage 9.

As you are working in a development environment, could you either debug (e.g. VSCode breakpoint with XDebug or just a good old var_dump(...); exit; this particular line (1200) in the WordPress core code of the site ((web/)wp/wp-includes/general-template.php in Bedrock sites)?
https://github.com/WordPress/WordPress/blob/5.6.2/wp-includes/general-template.php#L1200

What are the values of $paged and $page? Are these integers, strings or arrays?
Any plugins enabled?