Japanese Split-Leaf Maple Appears To Be Dying
Half of the branches look dried out and have no leaves on them. A closer look revealed some sort of fungus (?) growing on the branches (see photos). Some branches still have leaves but they appear paler than usual; on other branches, darker leaves are shriveling. There is new growth off the main stem. FYI, there's a very large maple tree whose roots are running through the bed where the tree in question is.
The light gray-green frilly growth on the bark is lichen, which is harmless. It's a combination of fungus and algae (which has chlorophyll and so it produces it's own "food.") It just uses the tree as a support. However, when you get a big increase of lichen on a trunk, it can be an indication that the tree is in decline.
We can't tell from the photos which branches/trunks are alive and which are dead. Once dead, wood is immediately a host to fungi and other organisms which begin the decomposition of the wood. They have nothing to do with killing it.
We do not see a specific insect or disease in your photos. So, your tree is dying from a cultural/environmental issue.
Prune out all the dead wood. Keep it watered in dry period this summer. It may revive with new shoots, slowly.
Many trees and shrubs have died or are declining because their site had standing water or soggy soil for long stretches last year. That drowns roots. If that's the case with your tree, try to divert stormwater in the future. If the tree has enough healthy roots left, it by regrow slowly.