My mouse acceleration recently becomes too fast.
Now I've tried changing it from 0.1 to 100, only to find that my mouse sensitivity is not affected at all

Same problem here.

I have a mouse with 1800 DPI, too fast for my '23 1920x1080 monitor.

0,1 to 2,0 not affects.

Nothing affects. Still at the same full speed.

I opened up a bug report:

https://bugs.kde.org/show_bug.cgi?id=365488