Is it possible to personalize the incoming call screen on my Xiaomi phone?

Assuming you’re talking about the global version of the Redmi Note 10 Pro that’s using the Google Phone app, it isn’t possible to have incoming call notifications in full screen everywhere on the Redmi Note 10 Pro.

This is how it works at this moment.

If you're in an app or the home screen, the incoming call will be shown as a heads-up notification.

If you’re in the lock screen, the incoming call will be shown as full screen.