Not much you can do. The rot fungus only works on wood that is already dead so what you have is a tree that is declining and beginning to die off inside.

Now this doesn't mean it will die tomorrow or a year or two, although it could.

The tree appears to be an Acer rubrum (red maple) and they only live for a century or so. Yours appears to be well on in years but could live 10-20 more years, although depending on the progress of the rot, could fall in the next strong wind storm.

You could have a certified arborist check the tree out and get more of a prognosis but that does cost $$.

I think the important thing is whether it will hurt anything if it falls, like a building, vehicles or people. If not you could just enjoy it for a few more years and figure tree removal into your budget and have it taken down soon.

At any rate, I'd plant a new tree nearby so when the old one goes, there'll be one with a good start, ready to take it's place.