I don't know because I haven't gotten that far in my studies of Ukrainian, but are there short-form adjectives like there are in Russian? I answered "я не голоден" and it counted it wrong. Can it only be the full adjective голодний/голодна?

How come hungry isn't masculine here?)

Спасибі, я не голодний

If I am in a foreign land, and can't remember how to say I'm not hungry, but can remember how to say I don't want to eat, I think that's close enough for me.