According to your screenshot, it’s obvious that you used Isotrim and after thatDeconstruct Brep, so if you use List Item with item index 0, you’d get the first one of the four vertices. That’s why you won’t be able to get the boundary vertices. If you use item index of 0~3, then you can get all of them, but as a whole, you actually get duplicated vertices across the surface.
Thank you for your answer.
May i ask how would you do it without getting duplicated vertices?
I thought using maybe a “dividing surface” component to get this points?