So I finally got it running with my Elcom BHT200!
Things needed:
BSR-200 Module as stated by Tobias and also Florian, thank you guys!
I soldered 2 cables on the front connections of the board (Blue and Purple Cable) you don’t need to solder it on the backside with the black coating.
Ring detection yellow to BUS+ as already mentioned but make sure to follow the procedure in the app precisely! (Ring - door not open - Ring etc. To let the Nuki learn the different voltages)
I am writing on my phone and edit this entry tomorrow with some proper images

I will make sure to show my exact wiring, at the moment I am using my quick and dirty setup which works
Ring to open + opening works like a charm!