Trying to transfer data from iPhone XR to new iPad gen 10, but iCloud backup is iso 17 and new iPad is 16

After you update the iPad to the current iPadOS you can then erase it and start the transfer using a method described in Transfer data from your previous iOS or iPadOS device to your new iPhone or iPad - Apple Support

To erase it, see the following from that support article:

1. Turn on your new device. A "Hello" screen should appear. If you've already set up your new device, you need to erase it before you can use these steps.* 

* To erase your device that's using iOS or iPadOS 15 or later, tap Settings > General > Transfer or Reset [Device] > Erase All Content and Settings. On iOS or iPadOS 14 or earlier, tap Settings > General > Reset > Erase All Content and Settings. This erases all data on your device. After you erase it, your device restarts and the "Hello" screen appears. 

Upgrade the iPad to the current iPadOS 17.0.3 first. See: Update your iPhone or iPad - Apple Support