Before running omv-release-upgrade, verified usrmerge is installed, then ran omv-upgrade, then rebooted.
The only error I saw is the grub-pc error.
I opened the web interface, OMV 6.0.30-1 is running.
Applied the changes.
Kernel is 5.10.0-0-bpo.12-amd64 (running on Xeon).
Shares are accessible.
What is recommended?