Expanding upon the excellent advice offered by Katana-San...
The Air2 is capable of update to iPadOS 15.8; the Air2 does fundamentally does not support iPadOS16 or later - as it lacks the necessary system resources (CPU and RAM) required for more recent major versions of iPadOS.
Be aware that the iPad Air2 was released in 2014 - ten years ago. All computers, Apple or otherwise, ultimately have a support lifetime and will eventually not be capable of update - and will ultimately lose support by the manufacturer and App Developers. Apple provides full update support typically for five to seven years, this being far longer than many other manufacturers.
Whilst many App titles remain compatible with your iPad, if you want or need to access to Apps requiring the most recent versions of iOS, you’ll need to consider replacement of your iPad with a much newer or current model that supports iPadOS 17/18.
For information, 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 15.8.3
iPad5, iPad Pro (9.7"/12.9" 1st generation)* - iPadOS 16.7.10
iPad6, iPad Pro (10.5"/12.9" 2nd generation) - iPadOS 17.7.2
(*) obsolete
Newer models are all able to be updated to the current version - iPadOS 18.1.1
- iPad Pro 13" (M4)
- iPad Pro 12.9" (3rd generation and later)
- iPad Pro 11" (1st generation and later + M4)
- iPad Air (3rd generation and later + M2)
- iPad (7th generation and later)
- iPad mini (5th generation and later + A17 Pro)
