Upgraded Ubuntu from 21.04 to 21.10, finally
Hesitating to upgrade #Ubuntu from 21.04 to 21.10 due to the bug of the ZFS driver included in the 5.13.0-19 kernel, I finally upgraded it because of the EOL of 21.04.
The error had been fixed on upstream, but the problem is that the kernel which the upgrade includes remains the same one, so the kernel panic occurred after the restart, which was expected.
My solution was to select the old kernel installed with Ubuntu 21.04 from the grub menu. This way you can run Ubuntu 21.10 successfully and update it, in order to upgrade the 5.13.0-19 kernel to the latest one thereafter.