Your account lives on the server you registered in. You can’t use it to log into other servers but you can interact with communities and posts in other servers (I’m from sh.itjust.works posting on sopuli.xyz). That’s my understanding anyways. I think the spinning button is a bug, I ran into it as well when registering an account
I’d like to know too. I’ve been using the free tier for years now and hosted a bunch of different stuff on it (no VPN though) and never had any problems