Quoting: RedjeI consider myself a casual user.
And I don’t really get the hype for flatpak. Me and friend of mine had several big annoying bugs. For example; in the steam flatplat my nvidia 3080 mobile was not working in games. And games installed outside flatpak worked just fine. And also apps just not working with flatpak, and local app just working as expected.

Flatpak is out there for 10years+ or so? And still such big issues…

This is a distribution or user issue not flatpak I'd assume.

Flatpak will install the required flatpak Nvidia driver runtimes automatically.

If you disable auto update in Gnome-Software or KDE Discover these runtimes will not be updated, apparently. As soon as your host system installs a new Nvidia driver package. Hence, the Nvidia driver is not "properly" installed for your flats.

Same happens with Mesa. Except that Mesa on the host can work with out-of-date Mesa in flatpak and does not require both to match the exact same version.

Simply run flatpak update and all your flats will work on your Nvidia GPU. Edit: Unless you have unloaded the Nvidia driver somehow by using things like prime-select. Which is unlikely as RTX 30 series do not require it anymore due to proper power management and offloading support since GTX 16 series and newer.