I was struggling with the same question, but I think I found a solution. Looks like after adding a target, you need to go to the shared folder and under each file, go to the identity and type area and add the new target to that file's attributes. I put it down in my response to my question below. apple forums link: https://developer.apple.com/forums/thread/666877 Hope that helps!

Though I think I have found a solution, I am not sure if it is the most efficient/best path This stack overflow link helped: Stack Overflow similar question - https://stackoverflow.com/questions/63048845/add-target-to-ios-macos-multi-platform-project-xcode-12 Essentially, after creating a Multi Platform App in SwiftUI: Add a new Target to the project (in my case watchOS stand alone) Click on "Content View" in the shared folder, and under Identity and Type on the far right, add the new target (in my case, watchOS WatchKit Extension) Delete Content View within the new target folder That will Build and run on my watchOS simulator! However, I still get some warnings: Warning: Error creating LLDB target at path ... using an empty LLDB target which can cause slow memory reads from remote devices. Though this gets me going a bit further, if anyone has a more efficient/better explained approach, please feel free to chime in.