Embed live camera in Keynote presentation
You can play your presentation in a window. This Keynote window can then go full screen with Photo Booth in split screen to one side, or as a normal window as you've been doing with Keynote in editing view.

To play your presentation in a window, choose Play &gt; Play Slideshow in Window (from the Play menu at the top of your screen).

https://support.apple.com/en-gb/guide/keynote/tana4da2681/mac