- boot into emergency mode (in the grub menu, hit “e”, and add ” emergency” to the end of the line starting with “linux”, then press ctrl+x)
- if needed, manually import your rpool in the initramfs prompt like you did in your first post (“zpool import -N rpool” followed by “exit”)
- enter your root password when prompted to enter maintenance/emergency mode
- disable the zfs-import-scan.service (“systemctl disable zfs-import-scan”)
- continue the boot (“exit” or ctrl+d)
now you should be able to install the update with the fix, and then re-enable the zfs-import-scan service (“systemctl enable zfs-import-scan”) and reboot the host. I would recommend regenerating the initramfs (“update-initramfs -u”). if you are still dropped into the initramfs prompt after that, I would be very interested in your “pveversion -v” output and your grub config (“/boot/grub/grub.cfg”).