These are for helios64. I think the OP was looking for helios4. The omv link gives a 404 when removing the 6.
There's a helios4 image for 26.2.1 (Trixie?) but I'm not sure it supports OMV.
The omv-release-upgrade script says "The system architecture armv7l is not supported.", and the Armbian page says "OMV (OpenMediaVault) can be installed on Armbian Bookworm minimal with armbian-config -> software."
Bookworm will be supported for another couple of years (2028-06-30) at least. Sadly, it might be time to consider a replacement.