For new Linux users choosing a distro IS choosing a desktop environment. Installing a new DE that's different from the default is not a day one Linux task, so the default for the distro is what matters. Yes. the DE is the most important factor in choosing a distro, but saying that means the distro doesn't matter is just fundamentally incorrect and unhelpful.
I don't thibk op intended to imply that new users instal a new DE on whatever distro they choose, but rather it's clunky to explain that they should prioritize DE when choosing distro. like, imagine a new users asks what distro they should start with, I believe op is advocating we say "anything that uses KDE by default" (or gnome or xfce etc). plenty of distros have derivatives that are basically the same but use a different DE, so it's pointless to suggest one over the other when a new user is just going to use the DE to do everything graphically anyway.
That'd be nice and all, but they still have to pick a distro. You can't just install KDE without a distro. A good KDE implementation just becomes one of their considerations. If you don't suggest one over another they'll probably just stick with Windows due to analysis paralysis.
On Ubuntu it's just sudo apt install kde-plasma-desktop. I guess that means you think it's even easier there and everyone understands all the implications of that and nothing could possibly go wrong?
There are no implications to installing anything in NixOS because you can go back to a previous state at any point.
Running the software might change your settings, but can't really do anything about that since that's the software author's choice and it's in your home folder
Look, I understand how NixOS works. It has nothing to do with anything I've been trying to say though. I'm trying to have a conversation, and you keep derailing it with you NixOS sales pitch. What do you even want from me? Fine. NixOS is the most bestest at everything ever and everyone should immediately jump right into it with no help or context straight out of Windows. Are you happy now?