Talked with Bob, who got instructions from Overleaf:
To get a template added to the page, there are two steps (1) get it into the Overleaf Gallery, and (2) let us know that you want it on the UChicago featured list. If it is already in the Overleaf Gallery, you just need to tell us the URL and we can add it directly to the portal page.
To get a template into the Overleaf Gallery, it needs to be uploaded or created in an Overleaf project and then submitted, using the “Submit” button at the top of the editor pane (see also here). If someone is submitting an Overleaf project for the UChicago page, it helps if they send us an email to let us know that it is going to end up there - we get a lot of submissions and review them all… so letting us know that this is for you will move it up to the front of the queue.
Basically, once we have them on Overleaf as templates we can ask Bob to ask Overleaf to include them in the page.