Got a new Pixel phone and you're excited to get it set up?

Steps to disable USB Debugging:

You can also find the "USB debugging" setting by navigating to "Developer options" in Android Settings, and then scrolling down until you find the "USB debugging" item. If you can't find "USB debugging" or "Developer options" in Android Settings, then this doesn't apply to you; you must not have enabled developer options.

If you attempt the Pixel phone-to-phone data transfer with USB Debugging still enabled on your old Android phone, the transfer process will reach the "Getting ready to copy" screen and will remain there, spinning away forever, waiting for you to go through the approval process on your old Android phone... but the approval process will never be initiated.

I would also recommend that you charge both phones before starting the transfer. The old phone will be charged by the new phone while the two are connected, and this can drain your new Pixel pretty fast. Plus, if you have a lot of data to copy, the transfer can easily take half an hour.