Hi Trey,
the answer is simple but "cruel" - the print feature was removed from Joomla 4.3 that's why we decided to remove it from Helix Ultimate template as well. As you know the offcial Joomla 3.10 support was stopped 4 weeks ago.
Theoretically you could add this code to the article view override code, but that's a task for you since you're still using J3.10. Sorry, I cannot help more with legacy mode.
BTW
(Thinking) Website guests anytime can click Print page using their browser's menu or by using keys: Ctrl+P (Firefox, Chrome).