Server disconnected - game doesn't launch

I bought the game a week ago, Steam, PC. Today I try to play and I now get this error every single time when I try to launch. I can't even get to the main menu. Always this error first:

For a while after this started I also got the error that steam cloud is not connected and my progress will be lost. This stopped again though. I spent an extremely frustrating 4 hours with support, nothing helped.

Nothing changed on my side from yesterday when it still worked.

Support said there are a few people affected by such errors, but not these error codes. They said there is no fix and I just can't play. Wtf?

Error code: 0:850008S:17862870170:-2146566144Q