I first bought Designer in 2018 then added Photo and Publisher i believe in 2019. I first noticed that my Designer files had the Photo Icon and extension and would not show the thumbnail view, I'm not sure when that happened.  I got a new Windows laptop last month and still had the same viewing/file issues. I did some research and discovered it could be a Onedrive issue where all of my files were stored so I downloaded all of my files to the laptop's hard drive and i could now see the thumbnails