> These commands worked for me, to get Postgresql and MariaDB database plugins:

I haven't tried this, but I'm familiar with pipx. It provides a higher-level interface, so something like this should work:

  pipx install sqlit-tui
  sudo apt-get install -y libmariadb-dev
  pipx inject sqlit-tui psycopg2 mariadb

Ref.: https://pipx.pypa.io/stable/#inject-a-package

> I don't know if that would have worked just as well with pipx or not.

I don't actually see anything in the GitHub instructions about system-wide installation? But yes, since version 1.5 (https://pipx.pypa.io/stable/changelog/#150-2024-03-29) Pipx can do a `--global` install that by default puts the managed venv in /opt and executable symlink in /usr/local/bin.