How do I know if my iPhone is hacked

All such messages are scams presented by criminals. Close the offending page and avoid sites that are involved in such bogus advertising tactics. Do not download anything based on such messages.

Phony "tech support" / "ransomware" popup… - Apple Community

The popup is a scam to steal your identity, your money, or both. Ignore it and see this Apple guidance→Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams and this video: