The first generation iPad Air is obsolete. Whilst some App titles remain available and compatible with your iPad, if you want or need to access to Apps requiring a more recent version of iOS/iPadOS than the iPad is capable of support, your only option is to replace the iPad with a much newer or current model.
Many mainstream App Developers only support the current and previous one or two major OS versions. You will likely struggle to find Apps that don't require iPadOS 14 or later.
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 15.8.5
iPad5, iPad Pro (9.7"/12.9" 1st generation)* - iPadOS 16.7.12
iPad6, iPad Pro (10.5"/12.9" 2nd generation) - iPadOS 17.7.10
iPad7 - iPadOS 18.7
(*) obsolete
Newer models are all able to be updated to the current version - iPadOS 26, or optionally if running iPadOS 18.x to iPadOS 18.7
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/M3)
iPad (8th generation and later + A16)
iPad mini (5th generation and later + A17 Pro)