Hi, is it safe to assume that the metadata.jar that is produced by the multiplatform plugin can be used as the compiled common sources?

That's correct. The metadata jar serves as the artifact for common code, and can be used as a dependency in common source sets. You will need an artifact for your target as well though.

thanks! It’s confusing that it’s not called common, also could not find any official documentation.

I agree.

I saw a discussion not long ago mentioning that it was called common at some point, but was renamed due to the fact there could be some additional stuff there in the future, so it isn't really just common code per se.

metadata.jar

doesn’t contain compiled common sources. All it has is the common API, represented with serialized metadata.