You will need to interrupt the stalled process with a forced-restart:
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:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.

After restarting the iPad, keep the iPhone away from the iPad. Allow the new iPad to complete initial setup without attempting to transfer data from the iPhone, or restoring a backup, to the new iPad. Instead, simply set-up the iPad using the same AppleID (now known as your Apple Account) that was used to set-up the iPhone.
When the initial iPad setup has been completed - including allowing the iPad to update to the most recent version of iPadOS if prompted - you can then reset the iPad:
Settings > General > Transfer or Reset iPad > Erase All Content & Settings
Having performed the reset, you can bring the iPhone back into proximity of the iPad to perform the transfer/restore from the iPhone if required.