Yes, University A will still have your full HS application and their decision on hand. Your college stats and ECs will be most relevant in the transfer decision as others have said. Whether or not the initial waitlist will be considered is unknown.
You could mention the initial waitlist in your essay. If you choose to do that spend one sentence on it. The essay needs to focus on why you want to attend the transfer uni and what it offers from an academic perspective that your current uni doesn’t. If you are certain you want to transfer make certain you have a balanced transfer list. Good luck.