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.
Smells like FUD to me.