My apartment comes with a wall-mounted microwave (KitchenAid KHMC1857WSS) that I clean periodically. While doing so, I see this component mounted on the right-side inside the microwave. It clearly has a dark discoloration, looking like it was burnt or blown out. The component reminds me of sandpaper because it appears to have a gritty surface.
I'm not sure what this piece is, but since it looks burnt and cracked am wondering if it needs to be replaced. Looking at the online user manual it's still unclear what this piece is. For instance, on page 6 of the above PDF, the section titled Replacement Parts, Accessories and Cleaning Supplies does not list any part name that pops out to me as being this piece.
What is this piece inside my microwave?