SUMMARY
(Apologies if this is not the right category, there are too many categories and I cannot seem to figure out which is relevant to the bug report).
Ever since the plasma 5.21 upgrade, 'long press key' does not work anymore. Pre-update, pressing and holding any key on the keyboard would have resulted in the key press repeating (e.g. If I held backspace, it would keep deleting characters until I release it). Ever since the update, this does not work at all.

STEPS TO REPRODUCE
1. Upgrade to Plasma 5.21 
2. Open any application that requires text editing (e.g. Kate).
3. Press and hold any character on your keyboard.

OBSERVED RESULT
The action is only triggered once.

EXPECTED RESULT
After a delay, it should have kept repeating the key press until I release the key.

SOFTWARE/OS VERSIONS

Operating System: Arch Linux
KDE Plasma Version: 5.21.0
KDE Frameworks Version: 5.79.0
Qt Version: 5.15.2
Kernel Version: 5.10.16-zen1-1-zen
OS Type: 64-bit
Graphics Platform: X11
Processors: 16 × AMD Ryzen 7 1700 Eight-Core Processor
Memory: 31.4 GiB of RAM
Graphics Processor: Radeon RX 580 Series

ADDITIONAL INFORMATION
I also experimented opening a Wayland session, I don't know if this has anything to do with this bug.