After updating to Debian 11, many problem in KDE

Hi list!

Last sunday I updated my PC from Debian 10 to Debian 11.
I use KDE/Plasma als Desktop-Manager.

Since the update I have often problem at login.
It appears a little window from startkde with the message "startkde: 
Could not start ksmserver. Check your installation."

Unfortunately I couldn't find any other detailled error.

I checked in Google and I see, many other people had the problem, but I 
didn't found any solution that worked for me... :(

Could someone help me?

Thanks a lot
Luca Bertoncello
([email protected])