Fungus at tree root, anyway to help this avocado tree?

Moved into a home with an avocado tree and very clay rich soil. We eliminated a ton of weeds, mixed in some soil amendments (Kellogg’s) and placed a weed blocking barrier all around tree. I’ve noticed the top branches of the tree haven’t really grown many leaves, and saw this fungus started to grow, which leads me to believe there might be more going on.

Any ideas why this is happening and more importantly, is there something I can do to help this tree?

Thanks in advance