@hypolite @xy @helpers Unfortunately, I can't troubleshoot anymore today. I tried switching to PHP 7.4 CGI from FastCGI but that didn't immediately solve anything (other than make the error more obvious: going to / attempts to redirect to index.php/install/install...etc)

I've been trying to use the release tarball because when I initially tried I got a mod_security error regarding .git... So, if and when I continue, I might abandon this subdomain entirely, start fresh with a new subdomain using regular CGI and try again with git and investigate the mod_security error.