SUMMARY
Pressing a modifier key like SHIFT and/or CTRL before dragging and dropping a file between two dolphin instances determines if the file should be moved, copied or linked to. This works in X11, but not in Wayland.

STEPS TO REPRODUCE
1. Open two different folders in two separate dolphin instances.
2. Press and hold SHIFT
3. Drag and drop a file from the first to the second dolphin instance

OBSERVED RESULT
A window pops up asking the user to decide if she wants to move/copy/link the file.

EXPECTED RESULT
File is moved to location in the second dolphin instance, without asking the user, as she already specified her intend to move the file by pressing SHIFT before the drag and drop operation started.

SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux
KDE Plasma Version: 5.24.5
KDE Frameworks Version: 5.93.0
Qt Version: 5.15.3
Kernel Version: 5.17.6-1-MANJARO (64-bit)
Graphics Platform: Wayland
Processors: 4 × Intel® Core™ i5-4670 CPU @ 3.40GHz
Memory: 15,3 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 4600

ADDITIONAL INFORMATION
This bug is similar, but not identical to 

https://bugs.kde.org/show_bug.cgi?id=432263
https://bugs.kde.org/show_bug.cgi?id=423031
https://bugs.kde.org/show_bug.cgi?id=388259