why not pre-displace or sculpt that? like bake it in the geo. you’d get actually geo without xtra computation for the displacement. anyway…
cvars to test…
“r.raytracing.nanite.mode” will use the highres mesh for shadows instead of the proxy. not sure if displacement is supported for that.
or…
“r.raytracing.normalbias” will mess with the normal contribution. try some numbers. if you go overboard on it, it may reduce overall shadow casting.
and… a welcome to the forum. : )