sudo apt-get upgrade is not working

[harastaivan]

Hello, thank you for you guide. It's a bit outdated of course so I got into some errors. When I try to upgrade packages:

sudo apt-get update
Hit:1 http://archive.raspberrypi.org/debian buster InRelease
Ign:2 http://raspbian.raspberrypi.org/raspbian buster InRelease
Err:3 http://raspbian.raspberrypi.org/raspbian buster Release
  404  Not Found [IP: 93.93.128.193 80]
Reading package lists... Done
E: The repository 'http://raspbian.raspberrypi.org/raspbian buster Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Installation of omxplayer and git therefore fails too.

I fixed it by editing sources.list to legacy raspbian source:

sudo nano /etc/apt/sources.list

Change it to:

deb http://legacy.raspbian.org/raspbian/ buster main contrib non-free rpi

Ideal solution would be to update the guide to use supported OS image, but this works too and could be added to the guide.