(sorry for drifting away from the OP)
I am using the compiler-directives all the times, but there are some glitches, for example the lib’ that has to be selected/defined manually for using cloud-sync under macOS and also the fact that one can’t use search together with top-buttons on iPhone (search-field is visible, but not the buttons… can also be done via compiler-directives, but it took a while to recognize that for me), and others.
BUT: I have one single Xcode-project for all of my apps! It just may take some time to find out…