For standard Safari (not technology preview) 17.0 on Ventura "Swap Processes on Cross-Site Window Open" is already enabled (and labeled Stable) for me. I did not enable it so it's possible Apple already enabled this and their description of how to enable etc. is out of date.
Edit: The below comment is correct, I was looking at a similarly named item "Swap Processes on Cross-Site Navigation" - it appears this is not enabled by default right now.
Edit: The below comment is correct, I was looking at a similarly named item "Swap Processes on Cross-Site Navigation" - it appears this is not enabled by default right now.