Anyone who is using an older iPhone or iPad is recommended to update their iOS software by Saturday (11:59 PM) or else their devices will be offline
What will happen if users of older iPhones or iPads don't upgrade their software by Saturday night?
The issue is tied to a GPS clock reset that causes the devices to lose track of time (among other things), a bug that was spotted back on April 2019. The date on the devices technically resets back to zero every 19.7 years and needs to be patched. Only iOS 10.3.4 and iOS 9.3.6 and later were fixed... so anyone using earlier versions will need to update.
If users of the older iPhones/iPads don't update their software, they will risk not being able to connect to the internet starting Sunday, November 3, 2019, at 12 AM. This includes users of iPad 2, iPad Retina Display, 4th gen iPad, iPhone 4S (earlier than iOS iOS 9.3.6) and iPhone 5 (earlier than iOS 10.3.4).
How to update your iOS software
Most users would have gotten an 'action required' prompt. If not, details on how to manually update are at https://support.apple.com/en-us/HT204204