ppa:librecad-dev/librecad-stable does not have a Release file.

> sudo add-apt-repository ppa:librecad-dev/librecad-stable
...
Reading package lists... Done                                                                                         s
E: The repository 'http://ppa.launchpad.net/librecad-dev/librecad-stable/ubuntu focal Release' does not have 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.

Can someone fix this?

Tom Dean