While I think it can be done in pieces, GitHub actions look like a nice step forward for migrating some of our existing Travis / AppVeyor, etc. CI builds.
For example, there’s a CMake ‘hello world’ that builds binaries for Linux, Windows, and Mac:
https://cristianadam.eu/20191222/using-github-actions-with-c-plus-plus-and-cmake/
repository is here:
I think the first step would be to move the Travis clang-format into an action.