Since updating Xcode to version 12, I get this error when uploading my app to the App Store.
ERROR ITMS-90733: "Missing architecture. Apps built with Watch OS 5.0 and later SDKs must contain additional architectures."
When testing on my devices all works fine.
I've tried adding arm64_32, as some suggested, but that didn't help.
The project compiled and uploaded just fine in with the last Xcode 11 version.
In my case it was the problem was that the user-defined setting VALID_ARCHS was in the project, even though I didn't refer to it in build architecture.
The way to get rid of it was to select my target, and scroll to the bottom of the Build settings where User defined settings are shown. Select the "VALID_ARCHS" and hit the Delete key.
If that doesn't work, select the project instead and do the above.