The last commit on that repository was 7 years ago, seems unmaintained. I wouldn’t recommend using this.
If someone decides to use it anyway, don’t use their udev rules. Just install steam-devices
or game-devices-udev
instead. If you don’t have those packages available in your distro, all rules can be found in the git repo https://codeberg.org/fabiscafe/game-devices-udev
rpm-ostree currently does not support DKMS, and it’s unlikely that’ll be implemented anytime soon, if ever. It does support akmods, though, which is the preferred way to build Kernel modules on Fedora. You could ask if the packager can build that way to support the Fedora Atomic editions.
If you need these Kernel modules now, I think your only option would be to build manually from source, but that has the downside of requiring a manual step every time the Kernel is updated.
Edit: there are a few issue reports already: https://github.com/pop-os/system76-dkms/issues/58 https://github.com/pop-os/system76-acpi-dkms/issues/16