wlr-randr won’t work for Plasma Wayland as KWin isn’t a wlroots compositor:
wlr-randr
compositor doesn't support wlr-output-management-unstable-v1
The same applies for the AUR’s wlr-randr-git package.
KDE developer Nate Graham explained why Plasma Wayland does not use wlroots a couple of years ago in this blog post:
In addition, the problem of fragmentation of effort is being solved by wlroots, a library of Wayland implementations that you can use to build a Wayland compositor. We don’t use it in KDE’s KWin compositor because we already did most of that work ourselves before wlroots existed, but it’s a big benefit to anyone writing a new compositor from scratch today.