STEPS TO REPRODUCE
1. Set primary monitor, (3840x2160) to 130% scaling.
2. Set secondary monitor (3840x2160) to 100% scaling to the right of primary.
3. Log out and log back in.
There's a n overlap of a few pixels on the secondary monitor from the primary background which can be switched opposite by clicking on the secondary monitor background. Second monitor is docked at (2952,211). Launcher menu will open on the secondary screen.
Monitors well separated and secondary position calculated correctly. The secondary monitor should probably be placed at (round(3840/1.3)=2954, round(2160/1.3)-1440 = 222). Launcher should open above launcher icon in the left-bottom screen of primary monitor.
Linux/KDE Plasma: Gentoo linux with plasma-wayland
KDE Plasma Version: 5.27.1
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8-r3
Just reread this, and the secondary is 2560x1440 of course, not 3840x2160.
*** This bug has been marked as a duplicate of bug 465850 ***