To sticky a Section in Squarespace, you need to do these.
#1. First, install Squarespace ID Finder and find the ID of Section.
In my example, we will have: section[data-section-id=”667f8bc0d90ab50817476436″]
#2. Use this code to Custom CSS box
section[data-section-id="667f8bc0d90ab50817476436"] {
position: sticky !important;
position: -webkit-sticky !important;
top: 0 !important;
}