Not sure about the mouse, haven't tested. But i had 22 notifications from Firefox and it scrolls just a little bit down the list - no more than 2cm on the screen. I can click/drag the scroller on the scrollar and it works, it's just the scrolling with the touchpad when cursor is over the notifications.
Just installed Arch so no idea if regression.
Operating System: Arch Linux up to date as of 01 Dec 2021
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.2
Kernel Version: 5.15.5-zen1-1-zen (64-bit)
Graphics Platform: Wayland
Processors: 8 × Intel® Core™ i5-8250U CPU @ 1.60GHz
Memory: 7,6 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics 620
*** This bug has been marked as a duplicate of bug 443840 ***