Physical Material on Landscapes Not Working

For everyone new to this post !
What you may need to do is :

  1. Go to your landscape collision settings.

  2. Set “Simple Collision Mip Level” to a value more than “Collision Mip Level”, example : “Collision Mip level = 0”,
    “Simple Collision Mip level = 1” (Simply doing that worked for me).

Voilà.