Is this object watertight rhino yes and Anycubic Prusa and F360 no

[davidcockey]

@Steve1

whats going on ?

It is non-manifold.
SelNonmanifold selects it.
Command: ShowEdges
Found 7845 edges total; no naked edges, 80 non-manifold edges

Explode the object
Select all the parts
Join
Result will be a closed polysurface without non-manifold edges. (At least in V8.)
Note: This proceedure works with the topology of this object. It may not work work with other non-manifold topologies.

@Steve1

I also pasted it into Rhino8 and turned on shaded and a progress circle appeared and kept circling eventually I killed it and used rhino5 instead !

Switching to shaded mode took a few seconds in V8 for me.