Plasma with wayland

Notes

If your sddm doesn't work with wayland, you can use x11/ly login manager instead.
If your mouse is invisible with wayland, export KWIN_FORCE_SW_CURSOR=1 in your environment.
The order of drm devices used by kwin is important. If hardware offloading doesn't work try to reorder it with KWIN_DRM_DEVICES env.

Export environment in Ly

Create a script with your desired environments.

Here is an example with useful environment variables:

#!/bin/sh
#export CLUTTER_BACKEND=wayland
#export SDL_VIDEODRIVER=wayland
#export LIBGL_DRI3_ENABLE=1
#export XKB_DEFAULT_RULES=evdev
#export QT_QPA_PLATFORM=wayland-egl
#export QT_WAYLAND_DISABLE_WINDOWDECORATION=1
#export BEMENU_BACKEND=wayland
#export WLR_DRM_NO_ATOMIC=1
export KWIN_FORCE_SW_CURSOR=1
export KWIN_DRM_DEVICES="/dev/dri/card1:/dev/dri/card0"
exec "$@"

Pass the script to the /usr/local/etc/ly/config.ini by:

# If null, no command will be executed
# Important: the code itself must end with `exec "$@"` in order to launch the session!
# You can also set environment variables in there, they'll persist until logout
login_cmd = /home/user/.lyinitrc