Interactions works by adding styles directly to the affected elements, so one approach to this is to design your accordion, and then have a small piece of custom CSS which opens just the first item, using CSS pseudoselectors like :nth-child()
When users click, that element-specific styling applied by interactions will be considered more specific and will override it. Just make sure you’re using the same technique consistently, e.g. hide/show, or div height 0. Chrome devtools is your friend here.
Your title mentions triggering the open on scroll which is a bit different. You might be able to trigger that item-1 open with a separate scroll interaction, or you can use custom JS to build that.