Apple announced that iPhone 5 will require updating before Nov 3 or iCloud, App Store, email, web and other services will no longer work.
Starting just before 12:00 a.m. UTC on November 3, 2019,* iPhone 5 will require an iOS update to maintain accurate GPS location and to continue to use functions that rely on correct date and time including App Store, iCloud, email, and web browsing. This is due to the GPS time rollover issue that began affecting GPS-enabled products from other manufacturers on April 6, 2019. Affected Apple devices are not impacted until just before 12:00 a.m. UTC on November 3, 2019.
Apple https://support.apple.com/en-gb/HT210712#925
The implication is that if you do not update before Nov 3, you will no longer be able to connect to Apple and will not be able to update the phone via the IOS updater, and you will have to restore it from ITunes on a computer. If you don’t have a current backup, that means losing data.
Apple is sending out alerts to iPhone 5 owners that their phones must be updated to iOS 10.3.4 before November 3. If the iPhone 5 is not updated in time, it will be unable to connect to the internet entirely, including web browsing in Safari, email, iCloud and App Store services. This issue is specific to the iPhone 5, which was last sold in September 2013. To keep the phone functioning normally, update to the latest iOS 10.3.4 update before November 3. If you miss that date, OTA updates and iCloud backup will no longer be possible as the phone will not be able to connect to the network. In that case, you will need to connect to a computer and restore with iTunes on a PC or Mac.
As reported by 9to5Mac
If, like me, you have an iPhone 5 sitting in a drawer as a backup phone, it would be an excellent idea to pull it out now, charge it up and get it updated.
I was a little alarmed that the updater advised that it “will have to take all the apps off the phone to update, but, trust me, I’ll put them back on again”. It seems to have kept its promise.
Why do I keep it? There’s one dodgy application that I use, for a Chinese company’s automated pet feeder. I don’t want this app on my daily phone or iPad, so I keep it on the older iPhone and only use it when I go out of town and have to set up provisions for “She who must be fed”