It seems like Steam is having issue, at the moment, if you can't login or are stuck in a loading screen, don't panic, I'm sure eveything will be back to normal soon!
If you're having issue, don't hesitate to comment here too.
Yep, seeing that with my deck and HoloISO desktop right now. Best advice is probably to avoid restarting, and potentially switch to offline mode if you're still logged in.