How to know if my iPhone camera is hacked?

There is no known way to hack an iPhone, much less the camera. As such there is no way to know one way or another.

Even the current hacking software in the news is said to leave no trace, so no way to know if it was used or not.

For what its worth, its exceedingly expensive to use, so unless you may be a high value target such as a journalist, government employee, or high profile individual, its unlikely you would be actually hacked.

When your iPhone’s camera is active a little green dot appears at the top of the screen. This indicator is hardwired to the camera so it cannot be turned off by software. Look for the green dot.

Of course the only way to really know is to put a piece of tape over the lens but you have to remove the tape is you want to use the camera. Not exactly convenient.

Throwawayaccount123 wrote:

Also, is all of this the same and true for iPads including the little dot indicating when your camera or microphone is being used

Yes. IPads running iPadOS 14 will have the same protection, and will show the green dot when your camera is being used.

First, see:

If you think your Apple ID has been compromised - Apple Support

then:

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Unauthorized modification of iOS can cause security vulnerabilities, instability, shortened battery life, and other issues - Apple Support

Delete spam calendars and events on iPhone – Apple Support (UK)

Your camera has not been hacked.

There was an article, yes. It was an obscure hack and Apple already fixed it 2 years ago. Still, you're not being hacked.