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...