I've searched X-Plane Support website, X-Plane forum and the User Manual. The only discussion I'm able to find related to this topic addresses "How to automatically load a situation at start up. There's no discussion on how to create the situation file. I'd like to start a New Flight, pause it, and then save that situation. It was easy and obvious in X-Plane 9 & 10, but not so in 11.
See if either one of these is what you want.
https://www.x-plane.com/2017/03/tutorial-saving-loading-flights-x-plane-11/
https://x-plane.helpscoutdocs.com/article/66-x-plane-11-10-situation-file-improvements