How can I use "clickthrough URL" to link to a very large photo?

Site URL: https://www.thezimaconfession.com/photos-moscow-ii

I have tried to upload large panoramas to my galleries. Instead of remaining full-size (which can happen with normal ratio photos), the photos are automatically resized. They end up being very small and completely unimpressive.

So, how can I link through to a full-size photo (or upload the full-size photo so that people can-right-click and open the photo in a new tab).

It seems that Squarespace cannot do this for photos uploaded to a "gallery" - however it can do this for photos that are uploaded to a normal page!! (There is an option - "design / lightbox"). Surely the whole point of a gallery is that it should showcase photos in an elegant way.

This is not very satisfactory - can I raise a ticket to get galleries enhanced to have this option?