I currently use an iPhone XR (launched four years ago in the fall of 2018), running the latest iOS 15. I’d guess it will get another couple iOS updates, assuming Apple doesn’t take a big resource hog jump with iOS 17.
It runs perfectly fine, no performance complaints whatsoever.
If there is something I miss, it would be the latest camera features. Not that the camera is bad because it takes great photos - it simply isn’t the latest. The iPhone 11 is the current “sweet spot” in Apple’s lineup.
Note that starting with the “X” iPhone models, general smartphone performance and features with each new model leveled off. That is, smartphones, like tablets and laptops before them, have become mature. Tech companies are really reaching for new advancements that average users will notice… and justify another $700-1,000 outlay.
BTW, my battery health now reports 88%. Probably with heavier than average use. I’m noticing that deterioration. An “average” user might not. So budget $69 for a proper while you wait battery replacement by the Apple store.