First I recommend you turn on Overlays > Face Orientation. It's easier and more pleasing to the eyes, and you can see if Face Normals are pointing in the right direction. You have to turn off X-Ray.
You can also try the Non-Manifold and Interior Faces options under menu Select >
Select All by Trait, but be wary that these options don't always work properly so use carefully. Options depend on the Select Mode (Vertex or Face Select Mode).
You can easily see the interiors of your model by selecting the outer face in Edit Mode and pressing H to hide faces. Use Alt+H to unhide everything. Now you can see some problematic areas.
Apparently you have interior faces which are non-manifold. Read more about Non-Manifold geometry here. Remove those faces.
Then you have this problematic vertex. It is correctly part of one face but not included in the other face. Remove it by selecting the vertex and pressing X > Dissolve Vertex
Then you have this funny interior face here. These faces should probably be deleted along with 2 bridging edges.