Hi,
I've found a solution for me.
I updated my Macbook back to Catalina and also updated the final DisplayLinkDriver (no Beta version).
Then I switched off the automatic change between the graphic cards when a power supply is connected.
Here is a manual how to do it:
https://support.apple.com/en-us/HT202043
After that all my programm are working properly again and also the internal macbook displays comes up again after the clamshell mode.