online stuff smattered everywhere. plenty of people still playing and i imagine a good handful also snagged it like i did when epic gave it away for a day. there's also older stuff like well placed safe houses and joke bridges on flat land or mountain peaks that have an insane number of likes so they must've been there for years.
also there's a page where you can see the players you've interacted with, your likes for them and their likes for you and it also shows last login date, and most of mine are online recently like me with some maybe last logged in in january, or late last year. i did see one who hasn't played since '22 but they've still got stuff in my world, too, so i think there's some playtime syncing where a bridge or whatever might actually be destroyed in their game if they logged in today but since it was there from hour 5 to 25 of their playthrough you'll get it at hour 5 and will stay if you repair it unlike they did. but that's a guess.
edit: for quick reference when you log in you get a summary of people liking your stuff and yesterday i saw "75 players are pleased with you, 7328 likes". so definitely still active. also no spoilers but there are a game mechanic or two that affects how many other players you are connected to, so your actions in game can determine how many people's stuff shows up, as well.