<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/scrollax@1.0.0/scrollax.min.js"></script>
<script>
$('.has-background').attr('data-scrollax-parent', 'true');
$('.has-background .section-background').attr('data-scrollax', 'properties: { translateY: "30%" }');
$.Scrollax();
</script>
<style>
.has-background {overflow: hidden;}
</style>
The above update #2 from https://schwartz-edmisten.com/blog/how-to-add-parallax-to-squarespace-7-1 seems to work fine without messing up the quality of the image