Add Raspberry Pi OS repo to ubuntu:
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Add this to the /etc/apt/sources file with nano or kate:
deb http://raspbian.raspberrypi.org/raspbian buster main contrib non-free rpi

Then in the terminal, entre these commands:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 9165938D90FDDD2E 
sudo apt update

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Date: January 28th, 2021