Many are around. All ? May-be not, some people would have moved to other places (discord, Mastodon, and more)
Welcome here, looks like you already got the federation concept and how to access communities which aren’t on your home instance, congrats. Remember that you’re part of the community and be the change you want to see
Sometimes, it’s a bit messy as you get 3 communities with the same name on different instance and only one of the 3 is active, but in general it’s works