Ganoderma adspersum (= Ganoderma australe) or Ganoderma applanatum seem likely bets in your corner of the world. A close up picture of the spore bearing surface would be instructive, as would a cross section.
What species of tree was it found on?
Does it have a waxy crust on the top? (Try heating it to see if it melts.)
Have you tried making marks on the spore surface underneath?
It won't be toxic and it
might have some of the medicinal properties of reishi.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli