checkboxClick property
Fires when the checkbox next to the series' name in the legend is
clicked. One parameter, event, is passed to the function. The state
of the checkbox is found by event.checked. The checked item is
found by event.item. Return false to prevent the default action
which is to toggle the select state of the series.
API Docs: https://api.highcharts.com/highcharts/series.networkgraph.events.checkboxClick
Implementation
HighchartsCallback? checkboxClick;