Can't Save or Export QuickTime Video on Catalina 10.15.3

I am having a problem with QuickTime on Catalina 10.15.3. This is on a 16-inch Macbook Pro (2019). I recorded a Zoom video, which automatically used Quicktime on my computer. I made a copy of the video and edited it -- all in QuickTime -- and followed the app's own Help screen for how to save a video. Command-Save led to Export-As, and all seemed well. I even told it to export to the QuickTime player on iCloud, as the directions also said.

But then this error message popped up: "QuickTime Player can’t open movie. The file isn’t compatible with QuickTime Player."

I've tried this several times, and it's bizarre. This is a QuickTime Video, edited in QuickTime itself, and told to export to QuickTime Player on iCloud. What is going wrong? By the way, I also tried saving this elsewhere in iCloud, where I normally store Zoom videos. The same error message occurs. Help?