We can't quite tell from the few leaves remaining that aren't close to the camera if this is a red-leaved Japanese Maple (our primary guess based on the foliage and seeds visible) or a red-leaved Norway Maple. (Our native Red Maple is not likely based on the traits we can see, but we can't rule it out completely yet.)

Japanese Maple can be susceptible to a few pests and diseases, plus any number of abiotic (non-living, related to environmental conditions) causes of decline can affect them as well. This tree looks quite old for a Japanese Maple, so long-term issues might be present like gradual wood decay from a years-old injury or branch or root structures developed into problems where tissues blocking nutrient and water flow into the canopy were slowly "choked" off. There is no treatment at this point that will directly reverse existing decline, regardless of the original cause.

We see lichen growth on the bark, which is harmless and quite common, but if any mushrooms or other fungi are emerging from the wood, this indicates decay of the wood in that area. The fungus may or may not have been responsible for the death of those tissues as sometimes they are secondary issues only, taking advantage of wood already dead or declining from some other cause.

We recommend having the tree evaluated by certified arborist to see how salvageable any remaining growth is. Some arborists are employed by tree-care companies but others consult independently. Diagnosis of an issue that arose years prior (often the case with tree decline as symptoms don't always manifest right away) can be challenging, so they might not be able to determine exactly what happened originally, though they can still look for sources of stress that can be addressed if they think the remaining growth can be saved. (Nothing can replace the dead wood, though, unless it is trimmed out and nearby healthy wood gradually sends out new branches to fill-in gaps in the canopy.)

Miri