Looking for advice

4th object is the result of doing trim with 1st and 2nd objects.
The thing is that 4th object must be solid, not open as it is now.
Tried doing “cap” but it was unable to cap object. (because it’s top isn’t planar)
Any ideas how to make this object a solid?

are you looking for a
(of labyrinth and the sphere ?)

if you work with trim you must also trim the sphere against the labyrinth, and then join everything to get a solid result. (this will give you the curved / “spherical cap”)
(all boolean operations can be done by trim, split, … , join)

There’s also BooleanSplit, which can be handy, when one of the operands is an open (poly-)surface and you don’t want to deal with surface directions.