sudo apt update error E: The repository 'http://ppa.launchpad.net/kirillshkrogalev/ffmpeg-next/ubuntu focal Release' does not have a Release file.
The solution in this link worked for me:
https://askubuntu.com/questions/65911/how-can-i-fix-a-404-error-when-using-a-ppa-or-updating-my-package-lists#:~:text=What%20are%20the%20causes%20of%20these%20errors%20in%20update-manager