There’s a couple of things you can do here
First I would check all face normals. Go to viewport overlays while in edit mode (small button at the top right in the viewport) and activate “face orientation”. All the face fronts will turn blue and the backs red, this makes it really easy to spot flipped normals. To flip a face normal, select it in edit mode, then go to mesh, normals, flip. Do that until everything is blue
Then make sure that you dont have any ngons or faulty geometry. Select a geometry, then go to edit mode, press shift+z to go into wireframe mode, press 1 to choose vertex selection. Now go to select, select all by trait, faces by sides. In the small window that pops up at the bottom left, choose in type “greater than” and at “number of vertices” 4, this will select all the ngons with more than 4 vertices in them.
If nothing works, try to delete the face and create a new one. You can fill a hole by selecting two edges and then pressing F
Once you’re done you can add the “Weighted Normal” modifier to fix up broken face normals
Hope this helps!