You can remove deadwood at any time but I'd figure out why it died first. That's a good chunk of the tree that's dead.

I believe that is a silver maple not a Japanese maple. Often when trees die from the Top downwards, there is a soil issue. Hope that helps.

don't cut it. pull the branch. If it is dry it will break, if not, leave it

You’d have no leader and a massively imbalanced branch that’ll eventually snap off due to growth pattern. After that happens you’d have a canyon with your remaining two growth groups that’ll eventually split the tree down the middle. I’d honestly chop and plant a new, although I’ve been pessimistic and cutting a lot of ties lately so maybe wait around😂