Previewing "geography" only works with map and layers, which are geographic. Layouts, on the other hand, are in "page space" and do not have a geography. I believe you are looking for a preview of what the layout looks like. This can be done as part of the layout's metadata.
You can create a thumbnail image of the layout by opening a view of the layout (the layout needs to draw first), then right-clicking the layout in the Contents pane and clicking Create Thumbnail.
This will create a thumbnail image of the layout that can be viewed in the Metadata tab.
You can also edit the layout's metadata to import your own images to be used.
Here is some help on thumbnails - https://pro.arcgis.com/en/pro-app/latest/help/metadata/create-a-thumbnail.htm
Hope this helps,