Update on L/R RC!
The best sounding option now is indeed L/R RC!

It sounds slighly more spacious and instrument seperation is more pronounced. (I only correct between 20Hz and 500Hz - maybe I expand that in the future further above, with a better microphone than iphone 12, but for now it‘s ok)
However, I am not only listening at one position in the room (large loft like room).
For other positions the stereo settings for bass were better - so I combined the two…

I used the L/R settings and replaced the settings below 100Hz with the stereo settings!

Happy!