Be warned: anyone who upgrades their iPhone or iPad to iOS 12 no longer has the option to downgrade. It’s not possible to go back to any version of iOS 11. Not that there’s much reason to want to.
iOS 26 is currently the latest iOS update, but Apple has quietly released iOS 12.5.8, a critical update for older iPhones, iPads, and iPod touch models that no longer support the latest iOS versions.