iMovie for Mac - Projects Thumbnails are Black Squares
I have just started using iMovie 10.2.2 on my new MacBook Pro running macOS Big Sur 11.1. I'm just learning how to use iMovie. I have created four projects and, while the creation of Projects appears to be straightforward, I do not understand why the thumbnails associated with each project in the Project View are simply black squares. I have read online that iMovie determines the thumbnail itself and that this cannot be changed manually. At this point, I would be happy with something other than a black square. See attached a screenshot.
MacBook Pro 13″, macOS 11.0