How do I know if my iPhone has been hacked?

Your phone is not hacked.

One or more of your accounts might be compromised if you let someone use your phone for a time and you also provided your Passcode to them along with your Apple ID and Apple ID Password.

iphones are rare to get hacked. Unless you have jailbroken it, there is no reason to assume that it is hacked

If you think your iPhone has been hacked, you can try this iOS Lockdown Mode

Perhaps if you explain why you think your iPhone might be hacked we might be able to help. If things seem to be not working right that is NOT the result of hacking. Hackers today are not interested in playing tricks on you, they want your money or your credentials so they can steal from you.

紀哥 wrote:

If you think your iPhone has been hacked, you can try this iOS Lockdown Mode

Lockdown mode is not something you do after the fact. It's designed for people in high risk situations who might be targets. If a phone had actually been hack (most likely not the case here), the damage would already be done.

I agree with this. Hackers aren’t into shenanigans. They want personal info/money