I have 0 idea why this might have happened
Because the system suspects your account might be hacked. Or any other reasons that, togehter, will make the system be suspcious. Suspicous enough to put the game in quarantine just to be safe. Maybe an updated file triggered a scanner. Or your behaviour matched a pattern that scammers used this week.
Any update can trigger this. For anyone. Bigger pages just get resolved faster in theory.
and I'm not sure what to do
Ignore it. Maybe do not update your other projects right now. But otherwise treat your project normally. Wait. Read more threads, like the sticky threads here. Wait some more. After several weeks, write a mail to support. Wait some more. After several additional weeks, post your ticket number here and state that you have waited 6 weeks now for quarantine to resolve.
If you have other socials, crosslink them. So that concerned visitors might validate if your account was taken over or is an impostor.
And just to be extra sure, you should check if you do not accidentally have cought a virus on your development system.
I'm completely stressing out
That might not sound helpful, but this is the wrong emotion. You should be annoyed. Not stressed out. Roll your eyes and sigh. It's the digital equivalent of being picked for a random search at the airport.
There is a lot of malware posted each day. I have seen hacked accounts by the hundreds. It's just the system trying to be careful. Your page is fully functional in quarantine. Aside from being temporarily unlisted and the quarantine message.
The advice for users would be, to put such games in a collection and check them out a bit later. As I said, there really is a lot of actual malware projects that are rightfully in quarantine.
some people see the quarantine and some don't
It's either in quarantine or not. The quarantine message appears only if you click a link or actually try to download something. Right up to the download button. It might not appear for you. I am not sure. You do not get the exact same page, since you are the page owner.