Did God harden the heart of Pharaoh

Ex 4:21 And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.

It was Pharaoh's choice to let his heart become hardened by rejecting God

The Lord gave him evidence of His power by working signs and miracles before him. The great I AM acquainted Pharaoh with His mighty works, showing him that He was the ruler of heaven and earth, but the king chose to defy the God of heaven. He would not consent to break his proud, stubborn heart even before the King of kings, that he might receive the light; for he was determined to have his own way, and work out his rebellion. He chose to do his own will, and set aside the command of God, and the very evidence given him that Jehovah was above all the gods of the nations, above all the wise men and magicians, only served to blind his mind and harden his heart. {CC 89.3}