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Unfortunately, your tree has classic signs of Armillaria Root Rot. This article will explain more:
https://www.gardeningknowhow.com/plant-problems/disease/armillaria-root-rot-control.htm

It does sound like it is suffering and with that much damage, you have a tough choice.

You can try to treat it and it may come back, but it may take years before it fully recovers, if it can recover at all. Or you can replace it with a new tree, which will likely take years to real that tree's size.

If you want to treat it, you can try spraying it with neem oil. It is both a fungicide and a pesticide and is systemic, so will be absorbed by the parts of the tree that you can reach to spray and carry it to the parts you cannot. This will cover many of the problems that could be affecting it.

I would also recommend that you have an arborist come and look at it. Tree problems are very difficult to diagnose without directly examining the tree.

Sounds like your tree is stressed. Has it been getting the equivalent or rain to 1'' a week? Have you been fertilizing, with what, according to package directions? Have you seen or seen signs of insects? If it's been adequately watered and fed with no insects, all you can do is wait it out. Your tree blooming is a sign that it's trying to survive. Just do all you can to help it. Is it in a container or planted in the ground? If containered, consider getting it into the ground...

Pruning helps keep plants, including trees, not only healthier but more manageable in size. While all plants have different pruning times and requirements, this does aid in focusing energy to other parts of the tree, such as new leaf growth or even root development for those newly planted.

I would be a little skeptical about tilling so close to your tree. This will likely damage the roots and result in problems for the tree. If you are having issues with tree roots showing through the soil or the root are becoming invasive, the following articles may offer some help: https://www.gardeningknowhow.com/ornamental/trees/tgen/exposed-tree-roots.htm, https://www.gardeningknowhow.com/ornamental/trees/tgen/problem-tree-roots.htm

The best time to prune mulberries is in winter after the leaves have dropped. Remove broken or diseased branches any time of year. I would not recommend any pruning once the tree begins budding unless you just have to.