Boolean modifier shows object as hollow at the cut out I am trying to cut out a tiny section from object (the red one) using Boolean modifier but when I do that it shows the object as hollow behind the cut out. But when I do the same with let's say Cube added from the Blender menu the cut out is solid - why?
Solutions I found around here talks about using Solidify modifier but that does not solve that for me: it just make the walls thicker but not doing the object solid and does not even respect the cut out shape (it should be like elongated ball as seen below)!
Can anyone tell me how to tell Blender that the cut out section needs to be solid and not hollow?
CLICK HERE FOR TEST BLENDER FILE

I am somehow starting to think maybe it is something with how is the object - LEGO brick - made, tho it is a standard official LDRAW brick repository DAT file imported into Blender, so it should not be the case (or I think it should not be thinking that anyone who made that 3D object known what he/she is doing when it is official brick from LDRAW). So maybe someone willing could look into possible design problems of the brick itself? Just a quick thought tho for those experienced Blender users (not my case).
EDIT
It turns out something unspecified was wrong with my Blender 2.90.1, once I downloaded and installed the newest version (v2.92.0) everything worked instantly as expected...but I will check the right answer anyway as ti basically correctly stated as of what to do to achieve the cut out itslef. :-)
I think your problem was that you never actually applied the modifier before deleting your carving object. Otherwise, as you can see, after I deleted your modifiers to restart with a fresh one, I could achieve the desired effect. I hope this helped.
EDIT:
Here's a .gif of the procedure:

delete the pending modifiers
create a UV sphere (scale it down and drag it around)
create a new modifier
apply it
delete the sphere