For those who face it in 2025, when there's no dedicated plist file for watch and tries to duplicate main app target and watch os app target - look at main target/General settings, "Frameworks, Libraries and Embedded content".

In my case "old" target's framework was sitting there, producing this wrong (as 50% of Apple's error messages) error message, and I even wasn't able to delete it using xCode UI - only by editing .pbxproj file directly by text editor. After that no runtime errors