quarterlife
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.
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.