For 2D avatars, I agree with what kionite said! VTube Studio is a great program that has a lot of good features and the tracking is great (iPhone tracking works best for it imo). If you want to get into making 2D models, I'd suggest taking a look at Live2D Cubism and if you want a discord community with more resources, take a look this one that's being handled by Brian Tsui (who's a great rigger).

I'm not sure about Unity/Unreal, that sounds more like 3D model stuff, which I don't really know that well. I don't think people have used that for avatar tracking, but sometimes people use it to modify 3D models?

No problem! Is there anything in particular you're looking for (finding 2D/3D models, streaming advice, debuts, etc)?