view xcf thumbnails
 

I noticed that nautilus cannot display thumbnails saved in gimp file format xcf.

I also notice that gthumb cannot even load let alone display xcf files. It is like they do not exist.

Is there any solution to this problem?

Is there any photo viewer organizer that can do this?

xcf is GIMP's native format. Any other program won't know what to do with those files, and thumbnails are definitely out of the question as xcf includes layers and channels and all sorts of other graphic-design-type mumbo jumbo data. Save the xcf as almost any other format and you'll get thumbnails in nautilus no problem.