My iPhone has an Apple Security notice about being hacked

It is 100% fake! Close the tab and follow the steps here: Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch - Apple Support.

Jack

It's not from Apple.

It's a malicious ad designed to scare you into buying useless software or steal your personal information.

Ignore it and install an ad blocker.

Sounds more like a scammer phishing for information.