Older version iMovie

You won't be able to get an older version of iMovie to run on OS 10.14.6 unless you had acquired a version of iMovie 10 at some time in the past, even if you later deleted it. In other words, you can update an earlier version to a more recent version, but you must have had the earlier version on your Mac at some point in time.

If the above situation applies to you, you can obtain a download of the highest iMovie version that Mojave will run using this procedure: To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the trash. (You can skip that step if you had iMovie 10 on your computer before, but deleted it.) 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 (if you moved it there) and return it to the Applications folder.

-- Rich