06-27-2020 03:31 PM
07-15-2020 02:25 PM
I found the solution via "apple support communities".
"OK, progress comes from poking about randomly, apparently.
It appears that if you create an empty project, the files in question suddenly appear to be usable, and iMovie happily lets you import media.
That question answered it seems."
It worked for me and I am just... at a loss for words.