Sorry for my unclear statement. After some homework with my TO I can say in fact I meant sudo -u nobody php-cli occ upgrade.
Because of the failed “occ upgrade” in my case I did a fresh installation of version 16.0.x.y and applied my backup files and folders according to official Nextcloud backup restore manual.
I needed to do an additional “patch” and my Nextcloud works like a charm after that.
Thank a lot to you all!
kind regards
Chris