Instead of solid mode with phong shading - I'd preview whatever 'lighting' artifact you think may have occurred in either lookdev/material or cycles viewport lit with a basic 3 point setup which would enable people too offer more effective feedback, if applicable?
Ok an N-pole shading error - (a vertex where 5 or more edges meet) which forces Blender to average face normals across different angles, causing dark spots or "pinching" artifacts when using smooth shading. And here's a few options that may resolve the problem 1. To fix the Normals and Smoothing often, shading artifacts…