if i i click "super" key while the mouse is on the secondary screen, the menu open on the primary screen.
If i digit anything, that should appear on the search bar, but it does not.
Interestingly, if i now open kmenu from the secondary screen, the search bar will contain the lost text!
So it seems the logic part handling the buffer understand correctly to operate on the kmenu of the secondary monitor, while the GUI display and uses the buffer of the primary monitor
STEPS TO REPRODUCE
1. add a secondary monitor
2. add a panel with Application Launcher on the secondary monitor
3. with the mouse on the secondary monitor, click "super" key (Application Launcher will open on primary monitor)
4. digit something, nothing will appear on the search bar
5. with the mouse open the Application Launcher on secondary monitor (search bar will have the text)
on 3., Application Launcher will open on the monitor with the mouse/last used window
on 4. no matter where the mouse/last application is, text should appear in the newly opened Application Launcher
Operating System: Arch Linux
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.89.0
Qt Version: 5.15.2
Kernel Version: 5.15.10-arch1-1 (64-bit)
Graphics Platform: X11
Processors: 8 × Intel® Core™ i7-4710HQ CPU @ 2.50GHz
Memory: 11,6 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 4600
*** This bug has been marked as a duplicate of bug 443131 ***