Last question first - you cannot restore an earlier version of iPadOS than is currently installed.
As for Outlook, delete the Outlook App from your iPad, then perform a forced-restart the iPad:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
After restarting the iPad, reinstall Outlook.