Manifold works on solid triangle meshes, OpenCascade is a true BREP kernel that represents solids as edges (straight and curved) and surfaces (not meshed) computed from those edges. There is no triangulation in the root model in OpenCascade.

So ... meaning Cadova has an underlying Mesh model, like OpenSCAD ... I wonder how they pull off proper filetting and curves.

Manifold is impressive, lots of info here:

https://github.com/elalish/manifold