So I have this mesh and I'm having issues figuring out why these are non-manifold geometries, I've pulled them apart, dissolved them, merged them by distances, checked for any faces that shouldn't be there or extra vertices / edges and I don't understand why these are being marked non-manifold, normally this wouldn't even be a problem because I won't be further modifying the mesh further, but I need to UV unwrap this to apply a texture to it in my game and that requires manifold geometry from what I understand, I also can't dissolve these edges to make the title look sleek and clean.
I've tried quite a few guides on non-manifold geometry and it seems like my entire model is derped both in terms of vertices and edges, faces are okay apparently but I don't understand what I did wrong, I just extruded and merged vertices by edges to make essentially all of it, and even if I had extruded extra edges and forgot to undo them I merged all the selected points manually and by selection by trait and neither produces any result so I don't imagine there are duplicate vertices / edges.
Any help for fixing and/or improving my modeling technique would be greatly appreciated, I've made a few models but this is the first time I've ever even encountered this sort of problem.
https://drive.google.com/file/d/1iqUoXQXGYPrqvPpo2CdKPBRoVGIl1vWA/view?usp=sharing
A link to the blend file