Is God's existence (metaphysically) necessary?
You mean to ask is God's existence necessary for universe to exist otherwise universe can't exist?
Or is God's existence necessary so people's life can have meaning otherwise life have no meaning?
A petty, illogical, irrational, violence, unjust, tyrant, malevolent God, is not welcome and not necessary to exist.
However, a generous, logical, rational, peaceful, just, not despotic, benevolent God, is welcome to exist.
Does that God's existence necessary for universe to exist?
Maybe yes maybe no, i don't know the true answer.
Does that God's existence necessary so people's life can have meaning?
If that God exist, he can give meaning to people's life.
If that God doesn't exist, people still can give/attribute meaning to their life by themself if they see fit.