On Wayland, KRunner always opens on a particular screen, when in X11 it opens on the screen with the mouse pointer.
STEPS TO REPRODUCE
1. In the Wayland session, with multiple monitors, invoke KRunner.
2. Move the mouse pointer to another monitor and invoke KRunner again.
KRunner always opens on a particular screen - in my case my notebook's screen, which happens to be the leftmost screen.
KRunner should open on the screen where the mouse pointer is, like it does on X11.
Operating System: openSUSE Tumbleweed 20211105
KDE Plasma Version: 5.23.2
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.14-1-default (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
Can confirm on Arch Linux (Plasma 5.23.3) as well as KDE Neon unstable, Krunner always opens on the left screen even if the cursor is on the right screen.
Still happens with KRunner 5.90.0 on Plasma 5.24.0.
Can confirm that it doesn't working on Kde Neon with 5.24.0
*** This bug has been marked as a duplicate of bug 427069 ***