no material are showing instead it takes a still color of the background in viewport I didn't use blender for quite some time then I loaded a saved file and saw that there were no material. I checked the material properties and they were all there but the viewport couldn't display them. I created new things and no matter what there were no material in the viewport in rendered view or material preview mode instead I see weird behavior when I zoom in and out it's as if there's a black thing of the same shape as the object that isn't affected by the zoom. and in the material properties menu the small balls that display the color of the material left of the material name disappear.
Could be that your normals are going wrong direction and the Backface cooling option is turned on. Check it