If I am not mistaken that option is only there for X11. Maybe that is the reason why windows are opening on the wrong screen on Wayland?
I guess wrong product, sorry.
There is no concept of a primary screen on Wayland *** This bug has been marked as a duplicate of bug 389016 ***
Sorry for the bug. I kind of suspected that already after creating it and reading the other bug. Then bug 425798 is probably rooted somewhere else (or just needs a different fix).