Hell Divers 2 has had a rocky relationship with Linux from the get go. Hopefully, as Linux gains market share, game studios start to include Linux testing.
I don't play it, but I remember that with each update, it sometimes broke for Linux, and sometimes it would fix the breaks. That was especially true closer to launch, though maybe some of those issues have been ironed out.
Are you using a Nix config you found, or is it something you cobbled together yourself? Gaming on Nix seems like a challenge!