Possibly are you not waiting for the export to complete. When you share out a project to a movie file a temporary file (or maybe two files) of zero size will be deposited on your desktop to aid iMovie in rendering the video. After the rendering is completed the temporary files will disappear and be replaced by the full sized rendered movie. Sometimes the temporary files will remain for a short period of time before disappearing. If you try to open them they will show no file size. Just wondering if that may be your situation. If not, read on below.
Since deleting preferences did not help, try redownloading iMovie. To redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash and return it to the Applications folder.
If still no success with importing, try the following procedures:
Safe Mode
Try booting up in Safe Mode (see Finder menu for instructions) and, after everything loads, immediately shut down and reboot in normal mode. Then see if iMovie works properly.
Resetting the System Management Controller
Try resetting the System Management Controller (but no longer available for the new M1 computers):
How to reset the SMC of your Mac - Apple Support
Resetting the NVRAM or PRAM
Try resetting the NVRAM or PRAM, although this issue would be fairly rare:
Reset NVRAM or PRAM on your Mac - Apple Support
Contact Apple Support
If none of the above resolve your issue, contact Apple Support. The techs there have the capability of remotely accessing your computer that we cannot do here. To contact apple support click on the Get Support item in the upper right hand corner of this forum’s screen. Navigate to a place where you can enter your phone number.
-- Rich
