God has no potentiality you say? You and I are on the same page when you say “God is pure act or actuality.” There is nothing for God “to become” or evolve to. He is already Perfection in BEING and lacks nothing. There is nothing for God to gain.
But where you and I make opposite turns is in your statement God has no potentiality.
An infinite perfection in being WHO is pure actuality can do all things that are possible. St. Thomas Aquinas puts it like this … “whatever is possible - is possible for God.” Thus in what is possible for God to do is His Potentiality. All of creation is contingent existence and depends on God to continue in being. Whereas God does not depend on anything for His existence nor does God “derive” His existence from anything. God SIMPLY IS all that HE IS in Perfection of BEING. Actus Purus. Within God’s Actus Purus is His ability to bring into being that which does not exist (ie - contingent existence). You and I need not exist. If God stopped thinking of you or me or creation for one brief moment - it would no longer exist. We derive our existence moment by moment by the sheer thought and will of God. The Psalmist writes “what is man that you should think of him?”
It is false to say that God has no potentiality. Actuality possesses potentiality - the ability to do or bring something into being that does not exist. What is possible for God to do - is Potentiality, but a Potentiality possessed by Actuality.
Please read the section out of the Catholic Encyclopedia on Actus Purus -
newadvent.org/cathen/01125b.htm
So that God is not a becoming, as in some pantheistic systems, nor a being whose infinite potentiality is gradually unfolded or evolved. But He possesses at once all perfections. He is simultaneously all that He can be, infinitely real and infinitely perfect. What we conceive as His attributes or His operations, are really identical with His essence, and His essence includes essentially His existence. For all intelligences except His own, God is incomprehensible and indefinable. The nearest approach we can make to a definition is to call Him the Actus Purus. It is the name God gives to Himself: “I am who am”, i.e., I am the fullness of being and of perfection.