Can't get Portfolio to show up when selecting a collection

Site URL: https://green-duck-kelr.squarespace.com/

Maybe I'm not understanding this right, but I've got a sample portfolio set up with 3 subpages however when I try to select that portfolio as a collection it says "There are no collections".

If I create a test blog collection I can get that to show up, not no amount of playing around with the test portfolio gets it to show up in the "collections" box when I am picking a source for the summary element.

Here is the sample portfolio:

No option to use it though 😢

Summary doesn't support Portfolio Pages.