-  Whonix ISO calamares installer shouldn't require networking for simplicity / usability. (No need to enter WiFi password / circumvention.)
-  Whonix ISO Live however should be able to go online.
EFI based systems currently require grub-efi-amd64 which would normally be installed using apt. This violates .
Installing grub-efi-amd64 and grub-pc at the same time is not possible since these have Conflicts: (in /debian/control) with each other.
But both grub-efi-amd64 and grub-pc are meta packages. These don't contain the actual grub binaries.
TODO: look at https://salsa.debian.org/grub-team/grub/-/blob/master/debian/control and install the actual grub binary package instead of the meta package(s). Thereby it might be possible to install both by default
Alternatively grub-efi-amd64 could be cached. (Similar to sudo apt install grub-efi-amd64 --download-only during Whonix-Host ISO build process inside chroot.)