To make Divi Theme's slider button links open in a new tab, you can add the following into the footer.php file (of the theme itself, or a child theme):

    $('.et_pb_more_button').attr('target', '_blank');

This is available as an option in Divi Booster. You can find the option on the Divi Booster settings page under "Modules > Slider > Open slider links in new tab".