Old iPad Air 2 would connect to Bluetooth devices but new one doesn't

Try these steps in order and stop if anyone works for you

1. Control Center - tap bluetooth off and on again - 8-10 times
2. Force restart the iPhone - After shutting down all open apps using the app switcher - invoked by quick double press of the home button and swiping up on each app till it flies off the screen. Hold the sleep/wake and home buttons down together till you see  logo - then release and allow normal boot up
3. Update to the latest iOS if not done
4. Settings -General - Reset - Reset Network settings will need to re enter WiFi passwords
5. If Apple pencil is connected - "Forget it" and try again
6. Backup the device to iTunes - Restore as NEW (not from backup) - see if problem resolves - if yes - restore backup
7. Make a "Genius" appointment at an Apple Store, or go to another authorized service provider.

What all did you try - the final suggestion was to take it into Apple 🙂

Mare sure that each device you are trying to connect is also in discoverable mode. Many devices, once paired to a device, have to be forced back to discovery mode to pair to a new device. The device's manual should say how to do that, but it's usually as simple as pressing and holding the devices power button until its status light blinks/flashes or changes color.