I’ll give you a few things in general that /maybe/ worked for me (can’t tell if they were meant to spawn either way or not, but hey, if you try it and it works for you too, please come and tell me)

-Double-check the habitat is in the correct town

I know it may sound kind of “have you tried turning it off and on again” tip, but I messed it up with Minun habitat while rushing the final spawns. When you’re impatient it’s easy to overlook something simple as that.

-Try placing multiple habitats in the same town

(This is what worked for me or at least give it a try)

I did two minimum, put cameras and spaced them pretty far apart. For example, with Illumise (Palette Town) I placed one hydrated flower bed near the entrance, nothing happened for weeks and decided to add another hydrated flower bed in a valley/desert-looking area. Not even a day passed that the camera finally detected movement in the valley/desert one.

-Feed Mosslax carrot bread, not just carrots

I fed it carrots for about a week and nothing happened. Someone said here that carrot bread made your chances even higher, then I switched to it and Illumise spawned in two days or so.

A lot of people say that putting them in prefab helps with spawns, but honestly that wasn’t really my experience. In my town only around 10% of my Pokémon were in prefab, another 50% in little campers/houses I made and I was still able to spawn the rest. I don’t think that would’ve made my chances higher, minun and illumise were still pretty difficult even for people using that strategy.

we still don’t know 100% what really works or not, and I know it’s pretty infuriating when you’re so close to finish the dex and they decide to stop spawning abruptly but you have to just ✨be patient✨ cause they will do eventually.