[FIXED]: drush The specified database connection is not defined: default

Fixing this took me years... I can't believe how long it took. The answers on stack overflow did not help.

The error was due to a mismatching php configuration for running in the shell ( /etc/php/8.1/cli/php.ini ) and in apache (/etc/php/8.1/apache2/php.ini ).

Specifically, I had to enable short tags for the shell: 

short_open_tag = On

With that, this particular error was fixed, and I was off to fixing the next error!