apt update: The repository no longer has a Release file

Solution 1:

In my case, I had several Ubuntu 20.10 Docker images running on my server. Due to the deprecation of Ubuntu 20.10, all of the PPA releases are gone.
I solved it by deploying Ubuntu 20.04 images instead and updating the packages for that version. I plan on deploying new images at 22.04, once that's been out for a while.

From experience, even though it's possible, it's not recommended to try downgrading the packages and PPA on your machine.

While this is generally a duplicate of What can I do if a repository/PPA does not have a Release file?, this is specific to Ubuntu deprecating versions in a generally unexpected manner.