*** Just to mention another fresh install of OMV6 on this SBC.
Thanks to all devs & Team
SD64GB + ARMBIAN Bulleyes CLI
Locales set to US english to avoid foreign Locales bug during install
Then for OMV install 
sudo wget -O - https://github.com/OpenMediaVault-Plugin-Developers/installScript/raw/master/install | sudo bash
next all the config fun !
installed the arm variant of proxmox on my Rock 5 and can confirm that an Omv6 install works fully in a debian VM with mostly everything working perfectly fine. Can even use the 6+ kernels with no issue asside from novnc not initiating a display for some strange reason.
Which kernel are you currenly running on the bare metal? I’ve yet to be able to get anything but 5.10 to boot on the actual board itself, and trying ti upgrade and switch the kernel over always leads to a nonbooting board.
This “Armbian bulleyes CLI” version i had installed states its kernel 5.1
The OMV diagnostic page returns :
Hostname
Version 6.3.5-2 (Shaitan)
Processor n/a
Kernel Linux 5.10.110-rockchip-rk3588
BTW *Would you know if this rock5B does support SSD drives, or only NVME ? thanks
Thanks for this!
I have this up and running with a couple containers going (adguard and a minecraft java server)