grub-probe understands Proxmox VE partitions but not Backup server

[Sasha]

Hi, guys!
I'd appreciate You for helping to figure out my case.
I have two completely identical hardware with clear by default installation of Proxmox VE partitions and Backup server. Here You are:

Proxmox VE

Proxmox Backup server

As You can note it's a difference in file system... And grub-probe notes it also:

Proxmox VE

root@hqm:~# grub-probe -d /dev/nvme0n1p3
zfs
root@hqm:~# grub-probe -d /dev/nvme1n1p3
zfs

Proxmox Backup server

root@bs:~# grub-probe -d /dev/nvme0n1p3
grub-probe: error: unknown filesystem.
root@bs:~# grub-probe -d /dev/nvme1n1p3
grub-probe: error: unknown filesystem.
zfs

Would You comment it guys? Is it a problem of Backup server installation or normal situation? What is this in fact?