As stated in the previous posts, the appearance of these types of mushrooms on a black locust is indicative of heartwood rot. And heartwood rot is incurable. The tree is dying but may take a number of years before it fails completely. The immediate concern is that trees with heartwood rot are structurally unstable and prone to wind breakage and dropping limbs. I'd consider removal if sited where it could fall on the house, cars or passersby.

Oh yeah. Many hollow oaks and others out there. Hmmm. Looks like your home is not quite clear. I votr for the have an arborist come inspect it answer. FWIW I am big on trying to read lines in tree bark. In White ash they make sense to me. Do I see an old prunig cut with a new branch comig from it right above the mushrooms? Then to the bottom right, something irregular. How high is that on the tree? And I like yo plant my replacement trees just outside the drip line of the old tree. Makes it easier on the tree trimmers (me!) and you do not have quite the forced timeline of planting it under the tree.

Why don't you check with the mycology society. It looks like no mushroom I have ever seen! Here is a link that might be useful: Mycology society

We-ell, you have some sort of bolete there, but boletus is a pretty huge genus. Some are delicious, some are inedbile and at least one is poisonous (and a couple are suspect) and they mostly look pretty similar. Narrowing down what it is could take some effort with a mushroom book. Sorry I can't help more than that! Cheers! Sunni