Dopus 13 has now become so complex that I can hardly find it out. How do I set mpg files to show as icon/thumbnails, avi and mp4 is displayed ok
Install MPEG-2 Video Extension from Microsoft-Store.
https://www.microsoft.com/store/productid/9N95Q1ZZPMH4?ocid=pdpshare
https://docs.dopus.com/doku.php?id=release_history:opus13:page4
If they still don't work after what Hardkorn suggested, make sure they work in File Explorer first.
Opus 13 and File Explorer get video thumbnails in the same way, so if they work in one they should work in the other. There's nothing to actually configure about them inside of Opus 13.
For other video types, similar components are listed here:
(It's Microsoft's choice that these are add-ons and not installed in Windows by default anymore. Probably saves them a few dollars a year or something.)