This is possibly due to a recent known issue::
Please see the items listed under Known issues and solutions of Stable Update 2024-10-10.
Specifically, look for the following heading:
- KDE Plasma hangs on Shutdown, Restart and Logout
To save you having to search too much, the workaround is to change your session settings:
System Settings → Session → Desktop Session → Session Restore:
Change “On login, launch apps that were open” to:
- Start with an empty session
Naturally, you might then need to reboot.
Regards.