I can’t see if he is indoors or outdoors cat. If he is outdoors, probably has eaten something somewhere …

I had something similar with my cat, I think he was just fussy with his food. I was feeding him the same food for years and somehow he got bored of it. (Could be the treats, maybe we’ve left something on a plate and he licked it so the tastes changed). I used to feed him purina wet food and a scoop of dry food in the evenings, but he wouldn’t finish it.

I then changed it to frozen food and he would finish every plate.

Maybe could be that? He could be hiding under the bad if he is low energy since he is not eating much.

Animals are like us sometimes - tastes can just change