Seems like this is a know issue, a workaround seems to be provided here to manually start the service without systemd. To better solve this issue, a Pull Request is waiting for review since one month here. Maybe you can try it out and help the reviewing process to go further?
To test it, the simplest is certainly to manually create the file cloudflare-warp.nix as describe here and add this file to your imports like:
I maintain cloudflare-warp. Yes, the problem is that the service, although contained on the package, will not work. The only way to use it on that case would be running the warp-svc on the background and then run the rest of commands through warp-cli. That’s why the module (the one linked by @tobiasBora) was created, to specifically move that service to /etc/systemd and make it available (which is why on NixOS it works differently compared to the other distros).
sudo nixos-rebuild switch instead appears erorr like this
error: builder for ‘/nix/store/h82pgsnl6a05s2bxw32bhy6vccgqdcp7-nss-cacert-3.86.drv’ failed with exit code 1
error: 1 dependencies of derivation ‘/nix/store/z2v318zraq18kg4j9qbx7wwyy3hp1fd5-etc.drv’ failed to build
error: 1 dependencies of derivation ‘/nix/store/ga0zw4rk5g026rbza93cc1xg0qlw3njp-nixos-system-nixos-22.11.1580.e285dd0ca97.drv’ failed to build