Thanks for the hint and for links. Now I can flash images, but at the end I get the message "No OS installed, press back button"! Although I can install RR normally via zip, but then it's over, I can not install a single Treble GSI, it always ends up in no OS installed.
RR zip is already installed, and partition is on it too. I can also install the image, even get the message that everything has worked successfully, but the restart comes the message "no OS installed"! during reboot, the phone starts in the bootloader!?! After that I can only flash the backup or reinstall RR-zip!