There is another issue with vmdb2 if you are using XFS. Starting with xfsprogs 5.15 (which is already in testing), bigtime is enabled by default, so that newly created XFS file systems won't be subject to timestamp overflow in 2038. Grub didn't land support for this feature until 8b1e5d1936ff ("fs/xfs: Add bigtime incompat feature support") in May 2021, despite the fact that XFS has had this feature for years and years and years.
So if you aren't using the latest security fixes, and you are using XFS as the boot partition --- it won't work on buster and bullseye. "Fortunately", there were were massive number security vulnerabilities in grub2 which forced a backport of grub2 2.06 to bullseye and buster, so if you have the security updates enabled, you'll probably be OK --- but it was only because of massive number of security problems forced that backport. In any case, a version of grub that will support the csum_seed feature will be landing in Bookworm in just a few days. So at that point, you'll be able to create VM images for Bookworm and Sid that will work with the e2fsprogs in sid. The current plan of record is that it will only be at that point that e2fsprogs will be allowed to migrate into Bookworm. For slowly moving upstreams like grub2, distributions *have* to take updates before grub2 finally gets around to doing a release --- to get security fixes if nothing else! The support for csum_seed has been in Fedora and other distributions for a while, since the patches had landed in grub2 in June 2021. I probably should have made sure the feature had landed in Debian's grub2 packaging earlier; that's my bad, and my apologies for that. Note that Debian's grub2 has well over 100 patches, nearly all of which are backports from grub2's git repo. So the argument that "there doesn't exist a formally released grub2 release" isn't particularly compelling, since all the distros are backporting patches. The only question is how *many* commits release has an individual distribution taken. By the way, in the case of the csum_seed feature, it's pretty straightforward to just run "tune2fs -O ^metadata_csum_seed /tmp/boot.img". If the UUID has been changed since the file system was created, you'll have to do this while the file system is unmounted and it will take a few seconds, but that's almost certainly not the case with vmdb2. - Ted