Could it be possible that normals are not in the right direction ?
( looks like Material view problem )
The normals seem to be in the right direction,it is okay in Maya but it messes up when I export it through FBX
did you check out the “materila view problem” post linked Material view problem ?
it specifically applies to maya, where it explains that “any kind of modifiers, especially copy, mirror, etc should be frozen/applied.”
(maya conversion to fbx loses some information, thus sketchfab cannot infer that some parts were from copy/mirror etc, whereas maya does know about it and fix it in their render)
With that line running from his head to his foot, it looks like a bad triangulation problem (Ngons!). Try triangulating your mesh before uploading
