It will never be a solid until you add the missing face and remove the faceless edge, ]I also recommend that you delete the guides, although that’s optional].
The missing face is only fixable with some triangulation as parts of its perimeter are not-planar.
It’s still not yet a solid.
SolidInspector² shows a nested group in one corner - select in the Outliner and explode it.
Then there are 14 surface border - i.e. edges without exactly 2 faces [probably around holes], and 104 internal face 'partitions. where some edges will have more than the 2 faces that are mandatory for a manifold solid.
So there’s still a lot to fix…
SolidInspector or SolidSolver cannot fix them.
Do it manually…
I suspect that starting again and keeping it simple would be the faster way forward !
The main form is actually quite simple - you seem to be making it more complicated than it needs to be.