Using the Split Tool to partition the solid is a good way of doing this. There are lots of ways you split the solid, but an effective option here is to create a sphere or box in the appropriate place (using the geometry primitives), then use that to split your solid:
I believe in all fem programs not geometry is important for solver but nodes and elements. We can have nodes and elements created directly without any geometry. I believe apex is same
Geometry primitives are treated as solids for the purposes of the analysis. It'll get flagged as unmeshed geometry in the analysis readiness tool, but of course you can ignore that.
