Open a Gallery (lightbox) from a button or hyperlink

Sorry other thread closed and I cannot reply.
@ Guenni007 . Script is not targeting the first_thumb but other image further down the gallery . If I change Content Element column count it will open a different thumb, but will be the same ones each time (not random).
Would you mind checking this please? Perhaps we could use the data-onclick=1 element or adjusting code to use First_thumb?

  $('.link_to_lightbox a').addClass('no-scroll');
    $(document).on('click', '.link_to_lightbox a', function(event) { 
        event.preventDefault();
        var linkTarget = $(this).attr('href');
        $(linkTarget).find("a.first_thumb").click();
    });