To solve the artifact issue after smooth shading in Blender, you can try the following steps:
Check the mesh: Make sure there are no overlapping or intersecting faces, edges or vertices in the mesh. Also, ensure that the mesh is properly aligned.
Apply modifiers: Make sure all modifiers, such as mirror or subsurf, are applied before smooth shading.
Recalculate normals: In Edit mode, select all faces and press Shift+N to recalculate the normals. This will ensure that all faces are facing the correct direction.
Adjust shading angle: In the Object Data Properties panel, under Normals, a
djust the Auto Smooth angle to control the threshold for smooth shadin