If all of your devices are up to date OS-wise, you need to disconnect your Apple Watch from your iPhone.
Then, Bluetooth connect the Watch to the iPad ( you do not need a watch app on the iPad, iPadOS 14.3 was released specifically to allow a direct Bluetooth connection of a qualifying Apple Watch ).
Once your Watch is connected to the iPad via Bluetooth, you can then go to the iOS App Store and proceed to download the Apple Fitness+ app and use all of its features.
Currently there is no direct AirPlay/screen mirroring from an iPad to any other smart TV or smart device using AirPlay2
Apple, currently has ONLY made this feature available to owners/users of an actual Apple TV box.
Best of Luck to You!