thx Justin,
I have copied 51-android.rules from
git clone GitHub - M0Rf30/android-udev-rules: Android udev rules list aimed to be the most comprehensive on the net to /etc/udev/rules.d/.
then
sudo groupadd adbusers and sudo usermod -a -G adbusers $(whoami)
after a reboot I connected the phone and a dialogbox on my phone ask me to allow the connection via usb and now it works 
:- 
the google 4a support ends in september and then I will try to get a LineageOS to run on it …