Fake pop up virus alert from Apple?

I just had this happen to me. I don't know how to make it go away. It acts like something is loading. There is a blue line going across the top pf the screen. I backed out of duckduckgo and shut my iPhone 12 mini off completely and rebooted it a few minutes later. When I tried to get back on the browser the pop up was still active.

It a malicious ad designed to scare you into downloading useless software.

Ignore it and install an ad blocker to stop seeing such ads.

It could be Phishing

• Beware of --> Phishing & Other Suspicious Emails 
• Know how to --> Identify legitimate emails from the App Store or iTunes Store 
• Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams —> Use these tips to avoid scams and learn what to do if you think your Apple ID has been compromised.

Ignore.

Keep the iPhone updated to the latest iOS always and never Jailbreak. That's it.

iOS / iPadOS devices cannot be hacked or infected with Virus / Malware / Spyware if it is updated to the latest iOS/iPadOS unless you have intentionally downloaded spurious software or unauthorized apps directly from the internet and installed on your device or/and have Jail Broken. 

It (Hacking) also depends on how careful are you in sharing sensitive and valuable information pertaining to your iPhone such as Passcode, Password etc with your friends and family members.

Be careful when sharing the device's sensitive and valuable information with friends and family members.

Thumb Rules:

1. Enable  Guided Access before handing over an iPhone to kids
2. Don't share Apple IDs
3. Don't Jail Break
4. Don't share sensitive information pertaining to your device and payment methods
5. Beware of Phishing

I had to uninstall the app. It became like an infected virus that produced the scam warning constantly. Could not simply quit the app to reset the problem. Duck Duck > Gone Gone