My iPhone videos

For some reason iPhone photos taken with the HEVC format are causing some issues lately with iMovie. If that is your situation, try going to your iPhone Settings/Photos/Transfer to Mac or PC and selecting Automatic. That will export your iPhone videos in the most compatible format for your Mac.

You can transfer them easily with Air Drop if you have that program enabled on both devices, providing that your computer and your iPhone are no more than 30 feet apart. Or you can transfer them in the way that you have successfully been doing in the past. That should still work.

-- Rich

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 iMovie will play a video that is dragged into an iMovie project timeline.

If still no luck, try using the free download, Handbrake, to convert the videos to H.264, Mp4/AAC, that Handbrake will do by default. Then drag the converted videos into the timeline of an iMovie project, and see if they play.

-- Rich

If still no luck after doing the procedures described in my previous post, do a redownload of iMovie. To do that, drag your iMovie app from the Applications folder into the trash, but don't empty the trash. Then sign in to the online app store and open your account by clicking on your name in the lower left of the app store sidebar. You purchases will be listed. iMovie should be among them and you can download it from there. If for some reason the download is not available drag your old iMovie app from the trash and replace it in the Applications folder. If the download is successful, you can empty the trash to delete your old iMovie.

-- Rich