Your model is not a manifold solid.

Change the way you view it to help yourself.

View > Hidden Geometry > On - you'll see lots of stuff that was hidden or smoothed.
That doesn't improve solidity tests.

View Mode > MonoChrome to remove confusion of a textured surface.
There are several 'flaps' and edges with only one face - every edge must have exactly one face.

Manually fix these errors and the object should then report as a Solid in Entity info.

To help identify the problem geometry I suggest you use Thomthom's SolidInspector2... and then doing a manual fix by editing it.
Using a Style with distinctive profiles and endpoints might help.
Also Xray mode would let you see what's a problem 'internally'...

My Solidsolver fails to mend it at all.
Fixit101 fixes somethings but then leaves it not solid !

PS: Delete the unwanted 'Sumele' figure as that doesn't help anything...