Can't figure out how to fix non-manifold geometry in my game title 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
You sure you merged by distance? I tried it upon first opening your file and it removed 195 vertices right from the get go (shown at bottom).

As you can see from the face orientation overlay, half of your mesh has faces facing inwards and the other half outwards. There is also a problem with the circled face (there may be a couple more instances). It looks connected, but it is in fact overlapping (you can tell by the z-fighting). This may be a result of the merge, but it needs attention nonetheless.

You can fix the normal direction by selecting all and then selecting mesh &gt; normals &gt; recalculate outside, but the face will have to be edited and &quot;re-connected&quot; manually.