How do I stop virus alerts on iPhone?

Hello~ They are scams. Don’t interact with them …just delete. Click on below…

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

~Katana-San~

Well, you would have to stop browsing websites altogether. You probably don't want to do that though.

The website is being paid to display the scam message(s), so lower quality websites are more apt to have more junk.