iPad Air 2 - Update on OS 14.4 not possible - why?

Do you have an iPad Air2 as suggested by the tags appended to your post, or do you instead have a first generation iPad Air?

Misidentification of an iPad Air1 for an Air2 is not uncommon. An iPad Air1 cannot be updated beyond iOS 12.5.1

Not sure which iPad you have? Identify your iPad model.

If your iPad is capable of being updated to a more recent version of iOS/iPadOS than is currently installed, these support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

If your iPhone, iPad or iPod touch won’t update - Apple Support

iOS update and restore errors – Apple Support

That’s great - you should be able to update to iPadOS14.4.

If having difficulties with updating, the provided links should get you up-and-running.