With an emphasis on the plurals in rods and cables. Most likely a fairly extensive network if you want to keep the tree together. I almost never recommend a support system without some pruning to reduce the load as well. You are likely a few thousand dollars into trying to hold together a tree that is falling apart. Is it worth it? Only you can answer that... How significant is it to the landscape? Does it have other historical value? But also look around: if it does fail, what is it going to hit?
Being that the OP was asking about mitigation only, that’s where my focus was.
A Mulberry of that size is a bit unique, at least where I am, so I was liking the cut of his jib, so to speak.
I’ve read Jeff’s stuff for years, and respect him as an arborist, but I think his reply is much to common.
When a client (or OP) asks for mitigation, that’s the direction I’m going to take until I know more about targets, or investment. Frankly, it refreshing when the conversation revolves around a mitigation first, cut second thread.
Of course, weight reduction pruning would go hand and hand with through rods and cabling.