How do I open this flush mounted kitchen light fixture?
It might be that the entire fixture is supposed to rotate a little and unlock from a base plate, but someone was lazy when painting the ceiling last time and didn't remove the fixture first, they just painted around it and got paint in the joint. So now it is being prevented from turning by adhesion to the painted surface. I would run a razor blade /Exacto knife around the rim where it touches the ceiling paint to break that bond.