Night mode on iPhone cameras came out with the iPhone 11. I didn't own an 11 as I waited for the 12 to upgrade from my Xs.
It was actually a bit more complicated than that. My Xs refused to boot in August. I needed a phone, so I bought the cheapest I could find: a refurbished iPhone 7. That got me through until I could buy a 12.
But I'm finding I really like night mode. Mostly (okay totally), I've used it to take pictures of my son's cat, Lily. In the evenings when it's dark, the family room gets gloomy and night mode works very well for taking pictures of Lily.
Lily likes to be next to me on the loveseat recliner. Usually she curls up and sleeps. But sometimes I can entice her with a snack to sit up and look cute, such as in this picture: