How do I know if my iPhone 12 has been hacked?

Keep it updated.

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 do not know how the accepted answer is appropriate to the question. The question is: how can I check if my iphone was hacked, not how to prevent it. Please Sravan, be sure to read again the question and adjust your answer accordingly.

[Edited by Moderator]

afoschalb wrote:

i do not know how the accepted answer is appropriate to the question. The question is: how can I check if my iphone was hacked, not how to prevent it. Please Sravan, be sure to read again the question and adjust your answer accordingly.

[Edited by Moderator]

There is currently no known method of remotely hacking an iPhone. If you were hacked, you would be a first in the industry, and therefore until analysis of your device was performed, no way to know how it happened.

There is no method to find out if you have been hacked, because it has not yet happened, so nobody knows how it would be done. There is no documented way of hacking and as such no documented indications of it, to tell if someone else would have had it happen to them.

If you believe you were hacked, then you would need to explain how it happened. As of now, there is no way to verify hacking, since there have been no demonstrable cases of it.

SravanKra’s answer is the correct answer. Keep your iPhone software up to date, never jailbreak it, and never let someone have access to it for an extended period of time, and you should not have to worry about being hacked.

At worst, someone figured out your username and password. But that has nothing to do with your phone. Change your passwords on your accounts and be sure that you use a different one for each online service.

It wasn't.

please elaborate your answer. explain how his answer is addresing the question specifically "how to know if my iphone was hacked?"

Why do you believe you were hacked? Keep your phone up to date. That's all you need to do.