The desktop keeps crashing when I open the app store or the dolphin file manager sometimes it crashes randomly what’s causing that issue
Good question. Unfortunately, without more information nobody can tell.
Which distribution are you using?
How experienced are you with using linux? Can you provide log files or a backtrace?
How did you install KDE on your Chromebook?
Do you mean you replaced Chrome OS with a Linux distro, installed something using the built-in Linux container option, or are you trying to use Crouton?
If you are using the Linux option found in Chrome OS settings (the most common thing), you really can’t run an entire desktop environment. It isn’t designed for that at all, just for running apps and terminal commands.
if you replaced Chrome OS, we will need to know what distro you installed, and maybe how you installed it.
In any case, we will need a lot more information.