The solution is to enabled encryption support in GRUB i.e. create a file /target/etc/default/grub.d/local.cfg with the contents GRUB_ENABLE_CRYPTODISK=y before the installer attempts to install the bootloader.
The solution is to enabled encryption support in GRUB i.e. create a file /target/etc/default/grub.d/local.cfg with the contents GRUB_ENABLE_CRYPTODISK=y before the installer attempts to install the bootloader.