I have enabled this option, and it works for .gif animations, but not for video files like .mp4, .mpg, .vob etc. when displaying thumbnails.
Is there some setting that makes them invisible?
Do you get sprockets for the same videos in File Explorer? (They will look different, but should still be there if the OS recognises them as videos.)
Back in Opus, if you go to Settings > File Types, then open the Movies file type group, is MP4 included in there?
It was not, so I tried adding it but it didn't make any difference.
Try resetting the Movies file type group, via the right-click menu from the file type list.
Make sure you don't have another group that the extension is also part of. Then close any open windows and re-open them to see if it's working now.
Thanks, I tried that but it didn't help.