removing the case clause terminator ";;" on line 19 of /var/lib/dpkg/info/grub-efi-amd64-signed.postinst allowed the installation to continue for me and complete the installation
removing the case clause terminator ";;" on line 19 of /var/lib/ dpkg/info/ grub-efi- amd64-signed. postinst allowed the installation to continue for me and complete the installation