Thanks for the hint! Will change that and try again.
The original installation was I think from 2013 or 2014. This is from a FOSS Project which got maintained over this time and since 2019 I maintain this project and do regular updates and stuff like that. So it seems back then the Plugin was implemented and has never been removed 
That did the trick! Your my hero for today 
EDIT:
sorry cant mark it as solution somehow