hi! there's lots of room for more input on this subject (particularly regarding the range of meanings in various cultures), but here are some previous posts to get you started
Did Romans in the Colosseum really use the thumbs up/down? and if so, which was live and which was die?
What's the deal with the "thumbs up" gesture?
In Ancient Rome, did giving a "thumbs up" really signify to let someone live?