This image uses a mesh with adaptive subdivision with a 4k exr file, and another mesh with a displace modifier using the same image and settings as the displace node in the node tree of the first mesh. The displace modifier could be applied, or not, doesn’t seem to matter. The second, proxy, mesh is high enough res to closely conform to the first, and it has the grass particle system. In the particle settings Show Emitter is unchecked, which makes the actual mesh invisible. Has to be done in two places for viewport and render. I think the result is quite satisfactory.