iMovie "Import Selected" button does nothing after recent update

iMac Retina 4k 21.5 inch 2017. BIG SUR 11.0.1

Two days ago, I updated iMovie to ver 10.2.2. It did the update ok. But when I tried to use it like I have been recently, it would not do anything when I hit the "import selected" button to import a media clip from my external hard drive, or from the internal hard rive - the Movies folder. . Prior to today, I have been using iMovie frequently to edit and piece together some old family video clips that I have had for a long time without problems. All seemed fine until this update.

Here is a screen shot - you can see, on the left underneath, the main screen that opens when I open iMovie. On top, on the right is the screen that opens when I click the import media arrow; then I highlight/select a clip; but when I hit the "Import Selected," nothing happens. When I hit Close, it closes to reveal the underlying screen.

Also, I have A MACBOOK AIR RETINA 13 INCH 2020 Big Sur too, and after the same update, it works fine, at least on the one video I imported, which is the same clip I tried to import from the same external HD as the iMac above!

Several other clips I tried to import on the iMac did not import - nothing happened, although when the import screen is on top of the main iMovie screen, the video clip is in the viewer part, and I can hit the play button and it plays. When I hit the "close" button to the left of the import selected button, that screen closes as normal and goes away, to reveal the regular iMovie screen. Please don't tell me my 2017 iMac is "outdated" somehow! O could it have something to do with the type of file. Again, prior to this update, I could import .dv .MOV .mp4 .m4v and others I think.

Thanks.