I’m sorry in advance but I’m somewhat new to linux. About 5 months ago I updated my system and I think in the process KDE updated as when I rebooted I was greeted by a new splashscreen and various other things. I noticed that my keyboard and mouse settings were unreconfigurable. I did some research and came to the conclusion it was a bug with KDE. Recently, I updated KDE again and this issue wasn’t resolved, which leads me to believe it might be an issue with my system. During this time I’ve updated to several kernels hoping that might change things, however nothing has come to fruition.
As it stands, when I reboot I have to open up system settings and move the mouse sensitivity down, hit apply, then move it back to where I want it for the desired sensitivity to apply. That seems to temporarily fix the mouse. For the keyboard, no amount of fiddling with the settings changes my input delay. I’ve recently found editing the delay with xset makes it useable, but I’d really like to fix the underlying issue. It also appears that passing -ardelay and -arinterval to xserverrc doesn’t address the issue either.
A while ago, I had similar problems in Plasma. In my case, it was the keyboard repeat rate and delay that wouldn’t persist across logins, a no longer working compose key, and the behavior of the numeric keypad.
Below is the link to my post on how I fixed things. Maybe you’ll find some inspiration in it.