One likely cause is a corrupt monitor profile.
Check the support page- Photos appear as black, gray, or blank rectangles in Lightroom
Followed suggestions in both links - issue persists.
I also note from your screen clip that the folder you are trying to import has .MOV video files in it.
I have read forum threads where this can cause import problems.
Can you try and use the operating system /Finder and separate the videos from the images- by moving them out to another folder. Then try the import of the images folder only.
And turn off 'Smart Previews'- these can be easily created at a later time.
The .MOV files were the culprit. Moved them to a separate folder and all's well.
I'm sure I'd have found it on my own sometime in April.
Thanks for giving me my life back./