It seems that not all iPhones do have this setting available. Not sure if this is related with the availability of RAW images, which is only supported on iPhone 14 Pro.
I may have missed something and had the impression that this was a "new" feature for iPhone 14 Pro only. But as the linked support documents mention, it is available on iPhone 12 Pro and later Pro models since iOS 14.3.
https://support.apple.com/en-us/HT211965