In a replit extension, is there a graphql query or function you can use to list the current users the repl has, and what users are currently online?
You mean multiplayer users?
At the moment you can’t test for online users, but you can get a Repl’s multiplayers.
See docs: https://docs.replit.com/extensions/api/data#repldatainclusion
If you can get all of the users in the repl, then it might be possible to scrape their profile page to see if they are online.
But they might be online and not on the Repl.