For large data sets you can consider using the Boost module - https://www.highcharts.com/docs/advanced-chart-features/boost-module It allows you to render large datasets efficiently by using WebGL. This can significantly improve performance for charts with thousands of points.

Another tip - have you seen the zones api available for line charts, which should be more performant and straightforward? The link to the API with the demo available there: https://api.highcharts.com/highcharts/series.line.zones

Let me know if you need further help with implementing any of these strategies!

Kind regards