God does not have or cannot have form. The statement is correct.

If you check the scriptures from all religions including Hindu and Islam they unanimously agree that

God has created this universe.
God established certain rules so that the universe lives its life.
Everything is controlled by rules given by God.
No one can challenge those rules.

For example, no one can be born adult, person has to grow up according to rules established by God.
No one can avoid death because it is a rule that the birth is always accompanied by the death of born person sooner or later.
There is no example since infinity that someone lived infinitely in this world.

It is God who implemented all rules by residing in each and every particle of his creation.
Since the world, hell, heaven are creation of God, the creator is beyond the creation, monitoring the creation. None of the object in the creation can compare with God and hence none of the forms created by God can emulate God, even though God is present in every form. One can very well worship God present every form and God present in whichever form according to the person's liking, but God is beyond those forms.

Hence the statement that God does not have form or cannot have form.

Now God is omnipotent too. He is All Mighty, meaning he can do anything and everything. He is supremely free to do what he wants, not to do what he does not want and to do whatever unthinkable that no one can imagine.

With this background, it would be most stupid to think that God can give forms to others but he cannot give form to himself ! It would be put limits on capability of God and no religion would agree that God has limited capability.
If it is the case that God cannot give form to himself, he would be like a coach of any sport team who can guide others but could not play himself with those skills. Is God like that?

Of course, NOT!
Then God must have form. And God does have form.

So, how to reconcile?
1. God does not have form.
2. God has form.