This problem is decades old (https://bugs.kde.org/show_bug.cgi?id=235630). Mouse speed is system wide and not managed by KDE, but it needs to be. A high DPI mouse simply leads to a terrible user experience. Using the xinput tool is a decent workaround, which could be built into system settings and set at login. https://askubuntu.com/a/569345/196639 For example: [X] Enable X mouse speed multiplyer (set at login) Pointer speed: [ 0.01 x ] <greyed out unless above is checked>
*** This bug has been marked as a duplicate of bug 311665 ***