Cabin main breaker on, cabin lights 1 and 2 breakers on (because I can’t recall which it’s on), then the button on the light fixture? Did you remove the fixture and confirm the switch and bulb work?
I don't recall on mine, but i wonder if that is on the AC side of the cabin lights? Try running generator and have port and stbd outlets breakers on. They operate some inside lights.
Otherwise you'll need to get the fixture down and test for ground and positive power feeds on the 12v side. Then trace up to the bus bar (neg probably) and positive (breaker probably) to figure it out.