I have a laptop with a monitor attached to it. On X11 the laptop screen is set as primary display, with my plasma panels and widgets on it, and nothing on the external monitor screen. When I switch to Wayland, the panels and widgets go to the external monitor, who is seen as the primary display in the monitor configuration module in Systemsettings. Changing the primary display to the laptop screen does not nothing.
There is no concept of "primary" screen in KWin. Neither on X11 nor on Wayland.
OK, but there is still a "Primary display" option in the Kscreen configuration module. And Wayland puts all my plasma element on the wrong monitor.
Created attachment 104352 [details] attachment-31310-0.html Please raise that to kscreen. The primary should only be presented on platforms supporting it.
I should not haev talked about "primary" or "secondary" screen. I should just have said "Wayland switches my monitors". It still happens in Plasma 5.10 beta.
I think this bug is irrelevant today.