2016 iPad Pro 9.7 inch not updating to iPadOS 14

Despite you question being incorrectly marked as resolved, lets see what we can do to help.

First, lets start with clearing up the true facts...

Your first generation iPad Pro 9.7” does support iPadOS 14.

Here is the full compatibility list for iPadOS 14.x; you will note that your iPad is listed here:

https://support.apple.com/en-gb/guide/ipad/ipad213a25b2/ipados

If you have already downloaded a copy of the update - and it won’t install - the update file may be damaged/corrupted. You need to delete the update package - and then download a fresh copy of the update...

To delete the failed update from your iPad:

Settings > General > iPad Storage

Scroll down the list of Apps until you find the Apple Update, tap, then select Delete Update.

After deleting the update, a forced-restart of the iPad is recommended:

• 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 an iPad with Face ID: 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, you can reattempt the OTA Update from iPad Settings:

Settings > General > Software Update

If the update continues to be problematic, these support pages may prove to be helpful with troubleshooting the problem:

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

If you see an error when you update or restore your iPhone, iPad, or iPod - Apple Support

I hope this proves to be more helpful. If not, please return to the tread - where experienced contributors may be able to assist further.