I launch it almost daily. Last Steam (on Linux) proper update was weeks ago. I think a new version of Proton was released like a week ago, though.

It's not a frequent occurrence, unless I have too many games installed, but then those are the downloaded games updating stuff, not Steam. Uninstall the ones you're not going to play in a while if that's becoming a problem.

Downloading the same browser engine that everyone else uses too time and time again as more bugs and security issues are found in it...

Wait, when is this occuring? I don't recall any installer downloading every other day. Is this something from maybe being on the beta branch of Steam or something? Or am I just missing this?