How to know if my iPhone has been hacked?

If I were in your place I would simply ignore these spam popups.

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 Jailbreak
4. Don't share sensitive information pertaining to your device and payment methods
5. Beware of Phishing

hacked- Said:

"hacked: Earlier this week i opened a link from the app “Pinterest” i was redirected to a website that clearly was not what i was looking for right before i deleted that tab i saw a message that said my iphone had been hacked[...]"

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Thank you fro the screenshot.

Report this to Apple:

Important: Forward your screenshot of this as an attachment to Apple using this eMail address: reportphishing@apple.com. In the comments pane, inform Apple of what the attachment is all about: an eMail containing an attachment of a phishing scam. Use my User Tip: Using the Photos App to Report Scams: - User Tips