GRUB Rescue booting Manjaro from USB
Without investigating much about this issue,
I downloaded today the latest Manjaro XFCE and charged it to a USB via unetbootin. When booting from the computer I entered a GRUB Rescue scenario after an “ERROR: unknown filesystem”.
Looking around, I recharged the USB with the .iso now with Etcher, which I haven’t heard about before.
Manjaro installed smoothly afterwards :-)