Apple today released iOS 12.4, but it turns out that that's not the only update that Apple released for the iPhone and iPad today.
iOS 9.3.6 and iOS 10.3.4 are now available for select iPhone and iPad models. The focus of these updates is to fix an issue that could affect GPS location performance and cause the system date and time to become incorrect.
These may look like minor updates, but a bug that causes your phone or tablet's system date and time to become incorrect would be pretty frustrating, so it's nice to see Apple update these older iPhone and iPad models that can't run iOS 12. If you've got one of the iOS devices named above, go into Settings > General > Software Update and grab your update.