Yesterday Twitter announced via version history notes in the Apple App Store that it is no longer supporting devices running iOS 11 or older on its official app. If you’re on iOS 11 will need to update to at least iOS 12 if you want to receive regular Twitter updates.
The current version of iOS is 13.5.1, with 14 still in beta and expected to release sometime this fall. The majority of iPhones, iPads, and iPod touch devices are currently running iOS 13, so updating to at least iOS 12 is something to consider doing if you haven’t already, as other apps may start to follow suit. Don’t fret though—since iOS 12 didn’t drop support for any devices, anyone on iOS 11 should be eligible for iOS 12.
You can update to iOS 12 on your Apple device easily in a matter of minutes by going to Settings > General, then tapping Software Update, and tapping Download and Install. Be sure to back up your information first, though, just in case.