Oh my gosh. Thank you SO much. That did work. :)

Oh, okay. So I added this to the functions.php: https://pastebin.com/yF0XzkHs

Then I add the following string to the end of the page’s URL: ?custom_ajax=116 (substitute the number at the end for the portfolio item’s number)

Is there a different way that I should try opening the portfolio preview on page load?