Thank you for the feedback.
I am playing around with the stock Pixel now, I installed RethinkDNS and disabled the Apps I do not need. I will try to check the traffic later after sometime in idle to see how many times does Google really phone home after I deactivated the telemitry as well.
Edit: I did not notice any strange traffic ongoing compared to the GrapheneOS phone.
GrapheneOS has Google photo and Camera without internet connection, I used it to take a photo and Google API measurements was used. I did the same on Stock and it is Play API instead, nothing more. I don´t know what more Data Play API would give Google.