Great work again @falk.
Note that GVM 20.08 (stable, initial release 2020-08-12) has some additional info on the changes between GVM 11 and 20.08 and AFAICS the --lock-file-dir /opt/gvm/var/run/ospd/ of the ospd-openvas service file should be changed to --lock-file-dir /opt/gvm/var/run.