Neither Apple’s nor Affinity’s documentation was precisely informative when I wanted to use MacOS Ventura’s Sidecar capability with my iPad and Affinity Designer 2.
Below is what I found worked quickly to allow me to draw on my iPad with the Apple Pencil whilst using Affinity Designer 2.
To preserve the iPad’s real estate, I leave the Designer tools and Studios etc on the Mac and use the iPad for drawing.
Separate Designer’s drawing canvas from studio controls etc.
Open Designer 2 on the Mac
Window >> Float View to Window
In the MacOS menu bar click on the Displays icon and then click
Mirror or Extend to >> Iain's iPad
Use as sparate display
Now slide Designer’s separated drawing window right out of the Mac display and thus onto the iPad’s display
Now I can select brushes and colours etc. on the Mac and zoom and draw with the Apple Pencil on the iPad