Why doesn't the RealPlayer library display the thumbnail images for the videos I downloaded?

To resolve this issue, clear your thumbnail cache:

1. Click the Windows Start button and type "disk cleanup" in the search field. Press enter.

2. Check the box next to Thumbnails and click/tap on OK.

3. Click/tap on Delete Files.

4. Disk Cleanup will now clear the thumbnail cache and close.

5. Restart your computer. The thumbnails should now appear in your RealPlayer Library.

Here are more advanced troubleshooting if the above didn't help.

https://www.windowscentral.com/how-reset-thumbnail-cache-windows-10