Is it possible for someone to access my camera on my iPhone XR?

Not likely at all. In fact, almost possible, unless you've jailbroken your iPhone. Are you someone who is important enough on the world stage for a government to even have any interest in something like this?

This is completely unlikely, iPhones are really difficult to be hacked

High millions....probably billions.....to one chance unless you are a spy, a foreign leader of a repressive government, etc.

Now, if you have jailbroken your phone.......that changes things.