I though’t i’d return to this with an improved answer. It’s still difficult to do this via Xcode main interface, as if you filter for .m and try and do CMD-A to select all, it selects the folders too, so you can’t add these to the target.
However, if you go to Project Settings > Build Phases > Compile Sources. You can click the + button, filter .m files, and you can CMD-A to select all here.
This works.
