I created a similar example with ACP 2023R2 and I was able to get the following mesh with the default solid model settings:
But, one problem is that the nodes in the regions circled in red are not connected and so this region can open up.
Note that in my model, I don't have any ply drop offs. Do you have ply drop offs in your model?
An alternative would be to create the solid mesh outside ACP, import the solid mesh in ACP and map the composite layup on the solid model. This way, you fully control the solid mesh (generated in Mechanical). You will find an example in the Ansys documentation here:
Let me know if this helps or not.