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Force restart of your iPad - as this will often clear an isolated software issue:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Have you installed then Microsoft OneDrive App on your iPad?

https://apps.apple.com/app/microsoft-onedrive/id477537958

Once installed, open the OneDrive App - and sign-in with your Microsoft account credentials. With the App installed, you should be able to enable OneDrive though the Files App sidebar.

The OneDrive App provides the necessary links for the native Files App to access OneDrive storage.

You're very welcome.