Finally upgraded the NAS's OS from OpenMediaVault: 7 -> 8; I held off on it for too long. The upgrade was a success, however, the EFI actually broke... which actually had nothing to do with OMV anyway.

The NAS was originally a build that ran on an ASUS P5N-E SLI board with an Intel Core 2 Duo E8400 -> Intel Core 2 Quad Q9550 with 4GB of DDR2-800 RAM and originally ran NAS4Free/XigmaNAS -> OMV6... from 2018. In other words, MBR/BIOS only, no GPT/EFI. This was getting long in the tooth by ~2024 (or 2025...), so the entire system was migrated to an ASRock J4125B-ITX board... which is EFI only. This necessitated a conversion from MBR/BIOS to GPT/EFI, as BIOS emulators never really worked right with this board.

The GPT part was easy... EFI, not so much. Needed to be chrooted in order to install some necessary packages and a grub-install command to be run.

I actually mounted the EFI partition wrong in /etc/fstab in the initial conversion, so it came back to bite me when I performed the OMV upgrade. The mount is proper now; it was missing the umask (umask=0077) entry.