iOS/iPadOS16 has introduced a new Rapid Response Updates - that provide a mechanism whereby an emerging threat/vulnerability can be addressed without releasing a full system software update. This feature is not available to devices that at are running earlier versions of iOS/iPadOS.
About Rapid Security Responses for iOS, iPadOS, and macOS - Apple Support
Whether or not you are able to update any iPhone/iPad to a newer version of iOS will be dictated by the device model - and the currently installed version of iOS/iPadOS. You can find this information here:
Settings > General > About
iPhone
Here is a list of the highest version of iOS supported by recent models of iPhone (for simplicity - “generations” are shortened to a number), older devices being restricted in their ability to be updated:
iOS16.5
iPhone 14 (all models)
iPhone 13 (all models)
iPhone 12 (all models)
iPhone 11 (all models)
iPhone X, XR, XS
iPhone 8 (all models)
iPhone SE2/SE3
iOS 15.7.6
iPhone 7 (all models)
iPhone 6S (all models)
iPhone SE1
iOS 12.5.7
iPhone 6
iPhone 5S
iOS 10.3.4/3
iPhone 5/5C
iPad
Here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:
32-bit devices (obsolete)
iPad1 - iOS 5.1.1
iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi+Cellular)
iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi+Cellular)
64-bit devices
iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.7
iPad Air2, iPad mini4 - iPadOS 15.7.6
Newer models are all able to be updated to the current version, iPadOS 16.5
- iPad Pro (all models)
- iPad Air (3rd generation and later)
- iPad (5th generation and later)
- iPad mini (5th generation and later)