Only the kernel module is open source, and it's just a wrapper for closed source blobs.
In actuality the open source drivers just kill all support for the 10 series, and otherwise do nothing to fix Nvidia's utterly fucked up driver problems.
Bazzite lead developer here, we actually never used the flatpak. Our first release had it installed in a distrobox container on the desktop images. Deck images always had RPM Steam because Steam is essentially functioning as a desktop environment there. We moved them both to be RPM for support consistency reasons.
Smells like FUD to me.
It's the same RPM that's installed in workstation from RPM fusion. There's nothing custom about that.
Gamescope is also an RPM, it's a slightly newer version than what Fedora packages but it's packaged the exact same way. Neither of those are likely to break because they are fundamental to the basic functionality of the deck images.
Additional pre-installed packages are added, but existing packages are not touched.
It's immutability comes directly from silverblue and kinoite, again nothing custom there.
I'm not sure what you mean by that, it's directly built on Fedora which is probably one of if not the best workstation OS.
The very first release was actually a steam deck release, the desktop release came later.
Until an iPhone can fold and send pictures/videos to people who aren't using the same phone that don't look like diarrhea I honestly don't care about anything Apple does.
Gamescope is broken on Nvidia and has been for years.
It currently breaks Firefox, but they're working on it.
Bazzite doesn't use flatpak steam. Standard rpm install with no sandboxing.
If you installed it that's entirely your fault.
For that, check out Bluefin or Aurora. They're all under the same umbrella as Bazzite, but with a user/developer focus instead of a gaming focus.