Try copying .env.example overtop of .env, without modifications. And re-run
php artisan optimize anytime you make changes in this directory.
If you still do not see the setup page, then it is a misconfiguration problem still. Possibly dependencies are not prepared.
It looks like I can see that your php-fpm is still not correctly configured… Are you sure you got php7.4 working properly? This screenshot shows /run/php/php-fpm.sock as a process, but your conf file for nginx shows /run/php/php7.4-fpm.sock.
You need to verify in /etc/php/7.4/fpm/php-fpm.conf that the
listen = /path/to/socket line matches.
You also must have the standard php-fpm running since the php7.4-fpm service depends on the main service php-fpm.
php-fpm with multiple versions is also not perfect. For whatever reason, you cannot actually have PHP 7.2 and php7.4 running/installed on the same system with invoiceninja.
Are you trying to run v4 and v5 on the same system? Because this is a technical restriction.