Folder thumbnail style

Hello, I would like to know how to set my lister to show the folders like the lower left 2 in this screen print versus the ones that look like open books. I don't know what I did, in both folders I have a small 600x600 .jpg that I named folder and it just shows up that way. Can I force it to display the thumbnails like the lower left 2?

image

I also have the same folder.jpg name in the other folders, so I don't know what the diff is??

Turning of shell/3D folder thumbnails under Preferences / File Display Modes / Thumbnails may be all you need to do.