Q.What Does It Mean When You Have A Hard Yellow Thing Growing On The Tree
Big hard and yellow.
Certified GKH Gardening Expert
It looks like an early Laetiporus mushroom. It is best to include all facets of the mushroom for identification, including the underside, for a good look at the pore/gill surface. This one will have pores, but the exact pore color will be telling of the species.
This will not be able to be treated, and it is eating the dead heartwood. It poses no immediate health risk to the tree, but will weaken its structure over time.
Here is an article that will help with bracket fungi: