Linux Servers are working, and fine so it seems. So we're happy to got that milestone done.
For Linux Client i'm very honest with you, we only got a single person working on build stuff and devops and we simply do not have the resources for a focus on linux there. You buying some invites for friends on linux - while i'd appreciate that - cannot change this. To pay another dev for this we'd need a hell lot more sales and linux is, as you're well aware somewhere at 1%.
Why it is not working for Proton i don't know - we don't check for Proton.
It not being mentioned in the announcement is indeed my fault, i had it announced on Discord but forgot it here in the heat of release day, you're absolutely right with this. I'm sorry for that. I tried to answer all linux questions immediately and with a link to the issue so you can follow it, though.
I cannot give you a serious estimate for release, we only have single person that can work on it. But it's tagged critical, that means it's supposed to be hotfixed. I'd personally love if it was hotfixed with 9.0.2 but i can't promise that. And i'd rather not promise something i cannot hold.