As far as I know HighCharts requires you to have an active license, as it is not free.
But more importantly, when looking at the documentation of Simple Charts:
This widget is based on a legacy library and is considered deprecated. It is not actively supported. It might work in Mendix 6, but it is not stable. If you want to contribute to the widget, or actively maintain it, please contact us!
So I suggest using ChartJS as that one is much better maintained and supported