I appreciate there are other videos for this, but this was made in 2019 so good if anything has changed.
BalenaEtcher (MicroSD Flashing Tool):
https://www.balena.io/etcher/
RaspberryPi ‘Do It Yourself’ Image:
https://retropie.org.uk/download/
ODroid XU4/XU4Q ‘Do It Yourself’ Image:
https://odroidarena.com/downloads/
RaspberryPi ‘Fully Loaded’ Images:
https://www.arcadepunks.com/pi-images-downloads-page/
ODroid ‘Fully Loaded’ Images:
https://www.arcadepunks.com/download-odroid-images-2019/
