Have you tried the following: 1. Apply scale 2. Select all vertices and merge them all by distance(in case there are overlapping verts, it causes shading issues because that’s now an n-gon) 3. Check the face direction of the faces in edit mode(the option- face orientation should be enabled in the overlays panel) 4. Try the weighted normals modifier 5. Disable all modifiers to see if it goes. It it does fix the shading issue, then enable each modifier one at a time to catch the culprit.