install_graphics_menu() cannot access mhwd
During install it seems like mhwd isn't installed before architect tries to use it to detect graphics drivers on the following line:
https://gitlab.manjaro.org/applications/manjaro-architect/blob/master/lib/util-menu.sh#L453
While I haven't been able to figure out exactly why this happens, using the "Chroot into installation" option and running "pacman -S mhwd" seems to fix it.
This might be a bigger issue as the chroot environment seemed to miss more needed packages.