I just had the issue and I think I finally got it
The amount of detail that the map is bringing to your mesh is defined by the gap between the level viewport and the render of the multires modifier ( so I did 1 for Level viewport/sculpt and 6 for the render)
Once the map bake I plugged the image texture into the base map of the BSDF and switched to the material preview mode of the viewport
Hope that it helps 😉
