Oke, took me a day to fix this. In case this helps anyone else, here's how I did it:
Template: Helix Ultimate v2.1.1
Add in your custom.css file this:
.body-innerwrapper {
overflow-x: clip;
}
In SP Pagebuilder, enter the following in CSS Class for the column you want to get sticky:
.position-sticky
Add in custom.css this:
.sppb-column.position-sticky {
top: 110px;
height: fit-content;
}
Adjust the top according to your wishes. Of course this only works if the other column has more content than the sticky column, i.e. more height.
In the Bootstrap 4.0.0 and higher releases, this option is is done using the sticky-top class.