The multiselect.isSelected() method determines whether an event is currently selected. It returns true if the event is part of the current selection.
DayPilot.Scheduler.multiselect.isSelected(e)e (DayPilot.Event) - item to check
Returns true if the specified event is in the current multi-selection; otherwise it returns false.
const isSelected = dp.multiselect.isSelected(e)DayPilot.Scheduler.multiselect.get()
DayPilot.Scheduler.multiselect.remove()
Event Selecting [doc.daypilot.org]