Back to basics really. I’d start by first looking in your error logs to see if there are any clues there.
It’s hard to be too specific where to look without knowing what your hosting configuration is (apache, nginx, docker, etc.)
Also, when you say you installed it via composer… was this a project you already have working locally, or did you run composer create-project on the server?
I’m self hosting with Digital Ocean, Ubuntu, Apache, using Plesk Obsidian.
Heres the plesk logs showing accessing the site home, followed by the admin attempt.
I’m guessing that my issue is related to permissions as I’ve run composer create-project as root on the machine. and to get the main site up ive had to change permissions of all the files using chown.
I’ve used root as when using as a basic user composer does not run. Composer noob here. Yes I saw the warning to not run as root, but what is one to do when it works but the former does not.