greenbone-feed-sync is in the sbin folder not in bin.
Second, as the gvm user is nologin, I cannot make the cron job run for them:
0 0 * * * gvm /usr/local/bin/openvas-update
This always gives a /bin/sh not found error. I wonder how to resolve this conflict… (In the previous version I built from source, I did not face such a problem, but I cannot either recall if the description of the cron job or the user type was different.