I thought this might be undocumented, but apparently apexcharts allows you to define this:
brush: { enabled: true, targets: ['candles', 'candles_2nd'] },
I found in the library code that it is actually handled like this:
var targets = w.config.chart.brush.targets || [w.config.chart.brush.target]; // 與單目標(biāo)選項的向后兼容性
Best wishes, Jim