Unable to remove flush mount light fixture
I would bet that it is being held on by paint.
The two screws should be the only mechanical fasteners.
Take a utility knife and cut the paint line between the ceiling and the metal of the fixture and then use a thin scraper to push in between the ceiling and the metal of the fixture to pop it free.
If you have a Habitat for Humanity Restore or a home salvage store  you can go and look through their used fixtures