I have spent hours upon hours trying to get gnome 40 on my nixOS version 23.11, I believe, only to either break my config or the system. Please give me clear instructions to do so as I can find such anywhere. I truly am sorry if this is annoying in a sense for it seems that I have not read any notes on NIxOS’s package manager. This seems to be the consensus among other Linux users like those who use Arch. I truly am a “noob”. Thanks!
You would need to create an overlay with the old packages and some dependencies, plus replace the NixOS modules, similarly to Gnome 3.38 on latest release - #3 by jtojnar. It is possible but probably too much effort – the difference is so large at this point, you would probably need to modify tens or hundreds of packages, fixing the failing builds one by one.