No poster frame in cropped iPhone and iPad movies imported to Photos for Mac; Set Poster Frame command grayed out
Since iOS/iPad OS 13, my iPhone and iPad movies that I've cropped on the device and then imported to Photos (3.0) for Mac (OSX 10.13) show no poster frame in Photos. What's worse, it can't be fixed with the Set Poster Frame command, because it's grayed out. What gives?
MacBook Air 13″, 10.13