Hello,
Welcome to our forum and thanks for contacting us with your question!
You can draw SVG elements on the chart using the render.
See:
https://api.highcharts.com/class-refere ... derer#path
Your problem, however, is related to some algorithmic difficulty. I prepared a demo that draws a path for each border line, but for presentation purposes, I created the simplest algorithm and it may not be optimal for many points.
Demo: https://jsfiddle.net/BlackLabel/eLft2oh4/
I used the Highcharts built-in select, so you select points by clicking, and to select more points, hold shift.
If you have further inquiries, you may reach out to me at any time.
Best regards!