Working around the desktop installer image requiring peripherals to complete.
Prerequisite
Raspberry Pi connected using ethernet
nmap -p 22 --open ip.x.y.0/24
ssh oem@ip.x.y.z
sudo pacman -Rns calamares calamares-arm-oem
sudo pacman -S manjaro-arm-oem-install
sudo bash /usr/share/manjaro-arm-oem-install/manjaro-arm-oem-install
A headless system with a GUI desktop is useless unless you can access that desktop from elsewhere.
https://root.nix.dk/network-notes/tigervnc-over-ssh
Cross posted to Manjaro Forum