In addition to the previous 13.5 to update to a newer, compatible device, Apple’s iOS 12.4.7 and for older devices that don’t support iOS 13. This includes the iPhone 5s, 6 and 6 Plus, and iPad Air (1st generation), iPad mini 2, & 3, and iPod nano (6th generation).
As of the latest iOS, the 12, patches, the iOS 12.4.7, it is by no means a major update with some new features and performance updates, only security fixes. However, some of these devices can be as long as seven years, at this point, and that is very important.
So, if you’re still using one of these devices, and still use it, it’s worth the effort to go to the Software Update section, and download the updated version.