The repository 'http://ppa.launchpad.net/mc3man/xerus-media/ubuntu disco Release' does not have a Release file. code example
Example: E: The repository 'http://ppa.launchpad.net/webupd8team/atom/ubuntu focal Release' does not have a Release file. 404 error remove
sudo add-apt-repository --remove ppa:mc3man/trusty-media