Unable to connect to database - cannot find error messages

Hard to say, do you have a ".env" file at the root of your project? Its content overrides your config files.

Actually, you SHOULD use that ".env" file instead of writing directly to app/Config/Database.php, because you can change configs between your different environments (development, testing, production, …) by simply having another ".env" in each copy of the project.

If my answer is no help, try to provide more details (I know it's a lot to ask, CI4 is quite secretive about why the database doesn't cooperate).