If I recall correctly the script that goes to desktop mode explicitly starts plasma. Though I think they want to change that behaviour in SteamOS 3.8 or 3.9 to be more generic.
The trouble is that on every update all the changes you did to system files would be removed.
So you’d have to install Niri to your home directory and change the scripts that launch it with every update. Nothing impossible just a little bit annoying.














Is that the woman Road to Empress is based on? It’s a pretty funny Chinese drama.