No native wayland with Plasma 6 on Arch v2.1
Btrfs-assistant 2.1 (built from AUR) always opens under Xwayland with Arch Plasma 6
QT_QPA_PLATFORM= and WAYLAND_DISPLAY=wayland-0
Running from the launcher results in xwayland.
Running from the commandline pkexec btrfs-assistant --xdg-runtime=/run/usr/1000 --display=wayland-0
results in xwayland.
I have also never been able to get btrfs-assistant to do my breeze dark theme either. If run from pkexec I get no theme, but with sudo -E I do. sudo -E fixes both themes and wayland.
Edit: The following will allow pkexec to properly do the theme and native wayland.
command="pkexec env DISPLAY=$DISPLAY WAYLAND_DISPLAY=$WAYLAND_DISPLAY XAUTHORITY=$XAUTHORITY XDG_RUNTIME_DIR=$XDG_RUNTIME_DIR KDE_FULL_SESSION=true btrfs-assistant --xdg-runtime=\"${XDG_RUNTIME_DIR}\""