I've got a really simple scene here. It consists of a sun light, a sphere, a plane, and the sun is projecting the shadow of the sphere onto the plane through a pane of glass. The shadow of the sphere should have a hard edge to it, but cycles is somehow diffusing the shadow and making it blurry. I've tried this in both 3.0 and 2.93.
Filter Glossy
to 0 and indirect clamping to 0 then it's not a particularly helpful answer. Even at 128,000 samples per pixel my basic scene with a pane of glass is unusable, in fact, Blender's denoiser actually somehow makes it look significantly worse. $\endgroup$