How to address 'My iPhone has been hacked' message on iPhone 16 Pro Max?

Your phone wasn't hacked, it is a scam message designed to get you to purchase unnecessary software or phish for personal information.

Read more about it here -

Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support

If you received a message that the earth was flat, would you believe it?

Why would you pay any attention to a message that someone (likely a robot) sent that you do not know and has no way to know what is on your phone?

Your phone has not been hacked. Delete that scam message. Delete any other messages like this that you might see in the future.

No one—not even Apple—can remotely "see" what is or is not on your phone unless you specifically give permission for remote access. That makes any message like that automatically bogus.