"Cannot Open" error message when saving Quicktime Recording

Have been able to do several QT screen recordings and then suddenly, now, on every recording, when you save or export, it appears to save and at the very end, a "Cannot Open" message pops up.

Another poster provided a solution -- go to the folder

/Users/<userid>/Library/Containers/com.apple.QuickTimePlayerX/Data/Library/Autos ave Information/Unsaved QuickTime

where you will find a package that you can open and then drag the .mov file to the desktop

That didn't work in my situation.

What did work was resetting NVRAM