Niantic has just rolled out updates for the Pokémon Go app, and one of the new features for iOS will let you run the game at higher frame rates. The Verge has discovered a new option that allows you "unlock your device's native refresh rate for higher FPS." It's not explicitly stated in the app's change log and probably falls under the "various quality-of-life improvements" the developer has listed. Also, the option is off by default, so you'll have to find it in settings if you want to take advantage of your phone's capabilities.
As the publication notes, Pokémon Go was previously capped at 30fps on iOS - players have had to employ workarounds to get their games to run at 60fps - but newer phones are capable of more frames per second than that. The iPhone 13 Pro, for instance, has a 120fps screen. The Verge says switching the feature on made a huge difference and made the game a lot more responsive. While Niantic may have been trying to cater to owners of the new iPhone, the option can also be accessed on its predecessors. It just may not work as well on hardware powered by older chips.
You can find the the feature in the game's advanced settings, which will show "native refresh rate unlocked" when it's switched on.