My iPad Pro 3rd gen battery drains quickly

There is NO Battery Health option for iPads as the batteries are so much larger and last much longer then any iPhone battery.

Have you tried,

For much newer design iPad models, without a Home button, try the new simple hard reset procedure for the new 2018/2020/2021 iPad Pros, 2020 iPad Air 4 and 2021 iPad Mini 6 models.

1. Press and release the volume up button.

2. Then immediately press and release the volume down button.

3. Then, press and hold the single sleep/wake/power button You will see the Slide to Power off button, but keep on holding down the power button until you see the Apple logo, then let it go.

Once you have performed all the steps, wait for a few seconds and your 2018 iPad Pro will boot up completely to the iPad Pro’s Lock screen.

Best of Luck to You!

What iOS/iPadOS version is this iPad, currently, running?

No issue here on my two iPad Pro 12.9" 3rd generation running iPadOS 15.0.1.

What do you see in Settings > Battery > battery Health > ?

And which app(s) use the most battery?