There is a lemmy nixos module https://search.nixos.org/options?channel=unstable&from=0&size=50&sort=relevance&type=packages&query=lemmy in nixpkgs which is functional. Or at least almost there in terms of ease of use. Even with experience, it still took me over an hour before I could successfully start my instance.
ofc this doesn't cover the host creation, and other details, I already had a server with NixOS running.
It is possible to deploy a lemmy server via a NixOS option. It's under services.lemmy, see https://search.nixos.org/options?channel=unstable&from=0&size=50&sort=relevance&type=packages&query=lemmy
You could always try to improve the packaging (there is an issue I had, but a ticket was already open and should be fixed at worst in the next version of lemmy, which was released a few days ago if I'm right)
Of course, everything that make NixOS server hosting will making hosting lemmy with nixos easier, but most of the trouble I had with setting up my server a few years ago was understanding how to configure and run the DNS server on it.