Not sure I would reinstall OMV just because of this. If you can chroot into the install, you can install another kernel.
I think OMV 7 is safe. I am running it on all of my systems.
Well this was a daunting issue for me to stumble into this morning, but thanks to your suggestions, I'm sticking with 6.9.11 for a bit longer. I was able to chroot in and install a new kernel as you said. I'll post my process here on the off chance somebody else runs into the same issue (or, more likely, I somehow do it again in the future).
On a side note, I greatly appreciate your dedication to this project and all the time you put into helping the community.
Boot into live Ubuntu ISO
Mount OMV system drive sudo mount /dev/nvme0n1p2 /mnt
Mount EFI partition sudo mount /dev/nvme0n1p1 /mnt/boot/efi
Mount additional filesystems for i in /dev /dev/pts /proc /sys /sys/firmware/efi/efivars /run; do sudo mount -B $i /mnt$i; done
chroot sudo chroot /mnt
Install new kernel sudo apt install linux-image-x-amd64
Exit chroot (ctrl+d)