Raspberry Pis are full Linux single board machines designed by the Raspberry Pi Foundation and made by Sony (and others). They're not really an embedded system.
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Download this: https://downloads.raspberrypi.org/NOOBS_latest
Get a fresh SDCard and mount it on your Ubuntu system with sudo mount /dev/sda /mnt
Unzip it then rsync the folder you've unzipped it to /mnt (which is where you've mounted your SDCard).
Note: Any requirement to use a crystal ball or mind reading will result in me ignoring your question.
Criticising any questions is banned on this forum.
Any DMs sent on Twitter will be answered next month.
All non-medical doctors are on my foes list.