@ben.boeckel Have you seen this project:
for cross-compiling macos executables on Linux? I have not tried it, but if it works, it would be a way to keep all the CI build infrastructure in docker containers.
If it is worth investigating, we would probably need Claudine to look at the Xcode/SDK license and verify it is a valid use of the license. (I suspect it would be although we might need to run the docker image on Apple hardware.)