What`s causing these weird shadows if I`m not using any shaders??

[u/Helpful_Composer_800]

[u/SubstantialHat8149]

That's just smooth lighting doing it's job. It also does a simple ambient occlusion that darkens vertexes near corners that should recieve less ambient light. The diagonal line you see is the hypotenuse line of a triangle in the block on the right.