Will 11 hours of continuous charging damage my iPad Air 5th gen's battery?

You have no cause for concern.

Your iPad will suffer no ill effects through being connected to its Power Adapter for extended periods - or even continuously. Your iPad will automatically regulate and optimise charging - and will not overcharge the battery. 

When used in kiosk applications - where external power is connected for extended periods of time - the iPad may modify its charging strategy and limit battery charge to ~80% of maximum. This modified charging strategy is designed to reduce chemical ageing that might otherwise occur if 100% charge is maintained at all times.

Nominal 100% charging will be restored when a normal charge/discharge routine is restored.

More information about iPad’s battery management can be found here:

About iPad and iPhone Charge Management Feature – Apple Support

There’d mean approximately all iPad Air 5th generation models are damaged, if that 11 hour charging were an issue.

Per Apple “iPad automatically stops charging when the battery is fully charged, so it's safe to keep your iPad connected to a charger overnight. Charging resumes automatically if your battery level drops below 95 percent.”

One good long luxurious pull-up-the-covers-and-hide-from-the-world weekend nap, and I’m out past 11 hours.

Yes, your iPad battery will degrade, inexorably, and inevitably. From use. From non-use. All batteries do. All computers, too.

Use the iPad and its battery for what you bought it for, and when — not if — the battery fails, replace the battery.

Or replace the iPad, if it’s no longer serving your needs.

With appropriate care, you should get five to seven years from the iPad, or variously more.

Appropriate care for your iPad? Avoid drops and dings, obviously. Avoid heat exposure, too. That’s bad for lithium polymer batteries. Modern lithium polymer batteries also aren’t fond of deep discharge, either; of completely draining.

Batteries - Maximizing Performance - Apple

Charge and maintain your iPad battery - Apple Support

Batteries - Why Lithium-ion? - Apple

Hello~ No…no harm done. Click on and read this user tip by *Lawrence Fin h*…

When to charge your iPhone or iPad - Apple Community

~Katana-San~

as long as you don’t make it a habit of charging for extended periods of time there should be no real issue. It is wise to unplug and let it completely drained before charging again, but I would not fret if it was a one time occurrence best of luck.