Error installing flatpack

After doing this:

   sudo add-apt-repository ppa:alexlarsson/flatpak
   sudo apt update
   sudo apt install flatpak

I am getting this error:

E: Your kernels are unsigned. This system will fail to boot in a secure boot environment.
dpkg: error processing package grub-efi-amd64 (--configure):
 installed grub-efi-amd64 package post-installation script subprocess returned error exit status 1
dpkg: dependency problems prevent configuration of grub-efi-amd64-signed:
 grub-efi-amd64-signed depends on grub-efi-amd64 | grub-pc; however:
  Package grub-efi-amd64 is not configured yet.
  Package grub-pc is not installed.

dpkg: error processing package grub-efi-amd64-signed (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of shim-signed:
 shim-signed depends on grub-efi-amd64-signed; however:
  Package grub-efi-amd64-signed is not configured yet.

dpkg: error processing package shim-signed (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
           No apport report written because the error message indicates its a followup error from a previous failure.
                      Errors were encountered while processing:
 grub-efi-amd64
 grub-efi-amd64-signed
 shim-signed
E: Sub-process /usr/bin/dpkg returned an error code (1)

I think it is a known bug in Ubuntu 18.04 with unsigned kernels. Will flatpack work anyway?