The patch "10_linux_zfs_grub_2.12~rc1.patch" worked for me in that I could "sudo apt upgrade" the system without the issues I posted in my previous comment (comment 6).

$ sudo apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
#
# You can verify the status of security fixes using the `pro fix` command.
# E.g., a recent Ruby vulnerability can be checked with: `pro fix USN-6219-1`
# For more detail see: https://ubuntu.com/security/notices/USN-6219-1
#
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
3 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] 
Setting up linux-image-6.3.0-7-generic (6.3.0-7.7+1) ...
Setting up grub-pc (2.12~rc1-4ubuntu1) ...
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: vmlinuz-6.3.0-7-generic in rpool/ROOT/ubuntu_via8pv
Found initrd image: initrd.img-6.3.0-7-generic in rpool/ROOT/ubuntu_via8pv
Found linux image: vmlinuz-6.2.0-21-generic in rpool/ROOT/ubuntu_via8pv
Found initrd image: initrd.img-6.2.0-21-generic in rpool/ROOT/ubuntu_via8pv
Found memtest86+x64 image: /BOOT/ubuntu_via8pv@/memtest86+x64.bin
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ...
done
Setting up grub-efi-amd64-signed (1.194+2.12~rc1-4ubuntu1) ...
Installing grub to /boot/efi.
Installing for x86_64-efi platform.
grub-install: warning: EFI variables cannot be set on this system.
grub-install: warning: You will have to complete the GRUB setup manually.
Installation finished. No error reported.
Processing triggers for linux-image-6.3.0-7-generic (6.3.0-7.7+1) ...
/etc/kernel/postinst.d/initramfs-tools:
update-initramfs: Generating /boot/initrd.img-6.3.0-7-generic
I: The initramfs will attempt to resume from /dev/vda3
I: (UUID=f29902c8-253f-4318-bf33-026715c7f5d4)
I: Set the RESUME variable to override this.
/etc/kernel/postinst.d/zz-update-grub:
Sourcing file `/etc/default/grub'
Sourcing file `/etc/default/grub.d/init-select.cfg'
Generating grub configuration file ...
Found linux image: vmlinuz-6.3.0-7-generic in rpool/ROOT/ubuntu_via8pv
Found initrd image: initrd.img-6.3.0-7-generic in rpool/ROOT/ubuntu_via8pv
Found linux image: vmlinuz-6.2.0-21-generic in rpool/ROOT/ubuntu_via8pv
Found initrd image: initrd.img-6.2.0-21-generic in rpool/ROOT/ubuntu_via8pv
Found memtest86+x64 image: /BOOT/ubuntu_via8pv@/memtest86+x64.bin
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ...
done

$ dpkg -l | grep -Ev '^ii|^rc|^ic'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                          Version                                 Architecture Description
+++-=============================================-=======================================-============-================================================================================