I really miss the ability to swap out KWin for a tiling window manager. I'm currently using Krohnkite and it's OK, much better than nothing, but after having used a real tiling window manager the difference is just too jarring. I physically need a desktop which is usable as much as possible both with the mouse and with the keyboard so I have to switch as rarely between the two as possible. Plasma on X11 with a tiling window manger was the perfect combo.
The solution would be either for Plasma to do something like River did [1] and separate compositing from window management, or for Plasma to make it possible to use Plasma widgets in other compositors. As it stands now I either have to make do with Krohnkite or go down the ricing rabbit hole with with River and Quickshell.