It seems the Determinate Nix installer supports Fedora Atomic and SELinux.
On topic:
I really like Nix and home-manager. I’ve mostly switched to NixOS because it’s more convenient for window manager setups than building ublue images imo.
Having to mess with containers for different dev environments and keeping the up to date is imo more annoying than creating a shell.nix
Also being able manage my dorfiles with home-manager and installing software declaratively helps in keeping the system free of clutter.
Many flatpaks are not aware of their sandbox and thus have a bad ux.
E.g. flatpak Steam can’t access SteamLibraries at a non-default location, unless the user manually allows the path through flatseal. The same is true for other similar apps which don’t use the file portal.
Issues like this are unexpected for new users and thus it can be argued that flatpak aren’t a good recommendation for new users. I personally disagree because most flatpak work flawlessly and work everywhere independent of a users distro.