FYI Apple, I have been searching all over the place for hours trying to figure this out. Wherever it is said that you can't preview macOS widgets, Google couldn't find it, and I couldn't either, nor is it mentioned in anything I could see in the WWDC videos about this topic.
Brandon_Gruber
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Same issue here.
Ok, it seemed to be fixed for me after a disabled wifi, and then went into settings on the phone and cleared trusted computers, then I said ok to trusting the computer again.