Sounds like we've made exactly the same distro-hopping journey. I went from Arch -> NixOS -> Ubuntu, and am now torn between Pop!_OS, Fedora Silverblue, or back to NixOS. I thought Ubuntu would be nirvana - just use the defaults, and use the computer as a tool rather than endlessly tweaking it forever - but it's less "just works" than I was lead to believe and I miss knowing the exact state of my system just from a set of nix files. I'd love to know if your Pop!_OS + Nix solution works.