Open HEIF and HEVC format files with Photoshop Elements 2020 and windows 10

Do you have a cloud account where you can upload the video file and give us a link?  Or, this forum may accept the file if you are able to attach it as a Zip file.

The error message is not unusual, and I have never seen a consistent method to fix it.  You can try uninstalling and reinstalling Elements.  And you can also try uninstalling/reinstalling the Microsoft extensions.  However, in the meantime, I suggest that you convert the video files to .mp4 format, using a free utility called Handbrake.  You can convert your files in batches.

If that doesn't solve the problem for you, perhaps post your question in the Premiere Elements forum.  The experts over there may have a better solution than I do.

. . .  and if the file can be imported into the Organizer, have you tried updating the thumbnail, using Ctrl+Shift+U?

Elements 2020 should be able to view the .heic files. 

And are you talking about the Organizer, the Editor or both?  If you are talking about the Organizer, do the files import OK, and its just the thumbnail that can't be seen?

Are you able to view the files using the Windows Photo App? 

Which cache files did you remove?  You may need to delete the thumbnails cache, but I'm not sure whether that will fix your problem. 

Can you attach a sample photo just so I can confirm whether the file will open on my machine.  (I only have .heic files from an iPhone.)

And also post a screenshot of any error message you are receiving.