> Try installing kde and gnome, then uninstalling both and check how many packages remain.
Sounds like a package manager or package problem. Competent package managers (e.g. dnf) remove unneeded packages and all their owned files. Albeit, I think with apt you need to do a manual autoremove to remove orphaned packages.
Not suggesting that they're equivalently powerful compared to nix, but this specific thing shouldn't be a problem with traditional package managers.
A common issue with most package managers is that if you have A installed, and then you install B which depends on C, and that C happens to also be an optional dependency of A, then uninstalling B will not uninstall C as C won't be orphaned (because of A).
That's interesting. I'm surprised. Just some cursory websearching and didn't see anything that gave a solution here for DNF at least. Funky! Seems like there should be a way to deal with this.
I'm a relative newbie with Nix, but I recently installed a Gnome extension through Home Manager, and then removed it again. It left some native functionality unusable because the install flipped a pref and the dev had forgotten to revert that on uninstall. They fixed it quickly and it was nice and all, but it's still somewhat unpredictable to me when I will run into such cases.
Sure it's simple, just like 80% solving the problem is usually significantly simpler than solving it 100%. Nix (and its generation) is the only package manager that actually works.
Try installing kde and gnome, then uninstalling both and check how many packages remain.
Nix can do that with the whole world with nothing residing.