Open mesh no naked edges yet has non manifold edges

Hello, Ive been struggling with closing this mesh. Its open, doesn’t have any naked edges yet has many nonmanifold edges. How can I close it?

Thank you.

It would be good to see what it looks like. But I would use the new Rhino 8 Feature: ShrinkWrap and see if that helps.

The ExtractNonManifoldMeshEdges command can also identify where those edges are.