enable Shadow pass
change Cubes material setup of Alpha mode to Blend.
create View Layer for
and one for all objects to composit Shadow pass
The trick here is Alpha Blend mode in material. Objects with Alpha Blend are not visible for Shadow pass ... technically Im not advanced in this area to explane ...
Alrighty...solution is much simpler than I thought.
Output Properties > Output > Color > RGBA
I simply did not have the output color settings to include alpha channels!
So in that case, holdout does indeed work in Eevee!!
In case anyone bumps into this problem:
This was being caused by the noob issue of z-fighting. I managed to find a work around by creating a couple big n-gons, adding a hook to the high-res geometry and then using a copy location restraint locked to the z axis.
This solution allows for having dynamic high-res deformation sitting on top of a low-res plane ...