NixOS framework support is in it's infancy.

If you don't mind getting your hands dirty with the command line, what you can do is boot from a well-supported distro's ISO, which probably means Ubuntu. Then, skip the Ubuntu installation and instead mount the NixOS installer ISO and go through the installation process; It consists of creating filesystems, mount points, building your NixOS system from a configuration.nix, and finally installating. All of this can be done from the command line.

I recommend installing the most minimal installation; A terminal text editor and just enough to boot to a login prompt and connect to the Internet. Once you can boot that minimalist installation, you can then proceed with installing everything else. Having a workining minimal installation will save you time.