Disabling parallax/jarallax for mobil devices

I’m using a w3 website template and I’m researching how to disable parallax (actually the template uses jarallax attributed to github) and I’ve tried several (many) steps and it’s not doing what the published steps explain. The only thing that works is to delete that line of html, which disables the scroll totally and the background images don’t fit as intended. What am I missing?