Dual Licensing a Swift Package - any examples?


I am hoping to open source the core engine for an iOS/macOS app I have developed as a Swift package, and I would like to dual-license it with a copy left license that allows hobbyists and academics to use it and learn from it, but a commercial license available on request for anyone wanting to publish a closed source app with it. I'm trying to understand the issues. I have not seen any Swift projects under the GPL license. I understand GPL/LGPL code is not (really?) useable on the app store. I am wondering if anyone knows of Swift projects which are dual licensed that I could take a look at? FWIW there are several binary Swift packages as part of the main Swift Package that I could keep closed source.