“Hey Siri” doesn’t work on my iPad Air after upgrading to iOS 13.5

Without knowing what every option in support you've tried is, have you done everything in this link --> If Siri or "Hey Siri" isn't working - Apple Support

Also, since this happened after updating your iPad, try a forced restart (recommended after updating iOS anyway) :

• Press and hold (& continue to hold) BOTH the Sleep/Wake button & the Home button.
• Continue to hold BOTH (ignoring any other messages that may show) until you see the Apple logo on the screen.
• Release BOTH buttons when you see the Apple logo and allow the device to boot normally.

Hello,

Try resetting iPad's settings in Settings > General > Reset > Reset All Settings. Be certain you do not select Erase All Content and Settings as this will erase all of your information. It is a good idea to perform a backup of your iPad prior to resetting its settings.

Hello,

What is your iPad’s exact model number?

Settings > General > About