Is this legit?

URGENT ACTION NOW NOW NOW URGENT PROTECT (10) VIRUSES: all that urgency means it’s a scam

Remote virus scan: lie. Virus scans are deeply intrusive, and websites cannot scan. If websites could scan, they’d simply steal everything directly, and wouldn't bother with the subterfuge.

Your iPhone contains built-in anti-malware, as well.

What is that? It’s usually an advert for a sketchy VPN product you don’t need and that won’t solve the problem (falsely) reported by the advert, but will badly solve a different problem you don’t have but badly solving it in a way that is perfect for collecting personally-identified metadata.

Close the tab or close the window, and get on with the rest of your day;

No. All such messages are scams presented by criminals. Close the offending page and avoid sites that are involved in such bogus advertising tactics.

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

It's a scam. The criminals who presented it may "just" be trying to sell you software that you don't need. Or they could be trying to get information they can use to access your bank account or credit card account. (Information that they might then turn around and sell to other criminals.)

FTC – How To Spot, Avoid, and Report Tech Support Scams