Hey stevland,
Thanks for your fast response!
I solved it. You gave me a new idea to think about that issue.
Its not completely tested but it does the job for now:
Possible Downside: I think it affects all Dropdown Menus. (But until now, not a Problem for us)
I just added the following to my Custom CSS Code:
.select2-container--default .select2-results>.select2-results__options {max-height:100%}
Again, its not really tested and im going to discover if its the best choice to just set the height to 100%.
But the idea should be clear.
Thank you again for your fast Help. Have a nice day!