Hello Pylon - thank you for not giving up.
As you saw I don't really know what I'm doing when changing the delay values. But I saw many other guys who divided these values to adapt from 1 to 8 MHz.
Now I tried to raise these values in 0.5 us steps up to 12/10 - but without success.
Your other hint:
I found some info about this library (name=wire, version=1.0, author=Arduino) in a file named "library.properties" - but I took the latest version from github. I decided to go on with Sonal Pinto's code which is very simple and straight and works (with Wire.h) on my Genuino.
Regards
deetee