After some more research, I found out that I picked an old version of the script and you really have to search for manjaro-arm-flasher and not manjaro-arm-emmc-flasher.
I still keep this video, as it helps you to debug things, just in case things go wrong. But my comments are not fair, as I picked the wrong script.
Here is the video that explains how to install an image on a micro SD card: • Pinebook Pro installing Manjaro Linux...
Download Manjaro: https://manjaro.org/download/
Install Manjaro on the eMMC: https://forum.manjaro.org/t/pinebook-...