OS image retirement policy at Github Actions

Some time ago there were macos 10.14 images but they were deprecated and removed, now the latest MacOS version is 10.15

I would like to know the policy for image removing on Github Actions specially for MacOS runners. When 10.15 images will be removed?

It’s important for projects which provide precompiled binaries(if you build your library\app on MacOS 10.14 it will work on MacOS 10.15 but not vice versa)