Apple fitness app

You need an Apple Watch Series 3 or later.

That is THE imperative piece of necessary/needed hardware.

Without it you will never get to download the Apple Fitness+ app into your iPad.

You need more that just the app.

Your iPad needs to be updated to the latest iPadOS 14.3 or later.

You need a compatible Apple Watch ( series 3 or later ) updated to its latest WatchOS version and, also, Bluetooth connected to your iPad before the iOS App Store will let you download/install the Apple Fitness+ app.

You need to have or purchase an Apple Watch series 3, or later.

No options.

Sorry & Best of Luck to You!`