I have exactly the same problem with my iPhone 13. I have to walk around with two iPhones in my pockets - I use my old iPhone XS only to take photos because they’re so much better.
I’m a photographer and it’s absolutely devastating to see your photos being destroyed infront of your eyes with the IPhone 13.
I’ve talked to so many different people from Apple, I went to different apple stores and all of them had no idea how to turn it off. I’ve tried everything!
I wanted to change it to an iPhone 14 because I thought it was only iPhone 13 that had that issue - but I’m chocked when I realised that iPhone 14 also has this auto enhancement.
I was then able to report the issue properly and make a complain where I could send screenshots of the issue and I had a call with people from apple. I told them that it’s absurd that this issue isn’t fixed when people have been complaining about this since the iPhone 13 was realised, and the dude from apple replies “I’m sorry that you think it’s an issue”… (!!!!!!!)
It’s ridiculous that a phone’s camera in 2022 has an auto adjustment that you can’t turn off. Makes ZERO sense.