I am using iMovie 10.1.14. I have lots of media on a couple external hard drives that I want to import. I click the import button and the normal interface appears. All my devices show up in the left nav and I can navigate to media on my internal HD. But when I click on any external drive, the main window, where you can normally navigate through folders, is blank.
iMac Pro
Which version of macOS is installed on your Mac? If you just upgraded to macOS 10.15 Catalina you are no longer able to use some older video formats.You may want to check the formats of your older files against this list: About incompatible media in iMovie for macOS - Apple Support
If your videos are no longer supported, convert them on a Mac, that is still running macOS 10.14 Mojave to a more compatible format.
Which version of macOS is installed on your Mac? If you just upgraded to macOS 10.15 Catalina you are no longer able to use some older video formats.You may want to check the formats of your older files against this list: About incompatible media in iMovie for macOS - Apple Support
If your videos are no longer supported, convert them on a Mac, that is still running macOS 10.14 Mojave to a more compatible format.
What is the format of the external drive? What type of media are you trying to import, and exactly where is it stored? What is the format of the media?
It possibly could be a defective cable or socket. You could try changing out the cable and using a different socket. Not likely it is a defective drive because more than one drive is involved.
Possibly a corrupt preference is at fault. Try opening iMovie while holding down the Option and Command keys and selecting to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. Now see if the import window reveals the media on the external drive.
Also, try using the Image Capture app on your Mac to import the media to a folder on your desktop. Then drag the media from the desktop into iMovie.
-- Rich
Can't see any folders or files when trying to import from external HD
