As I look into the code, the exceptionDate option is actually not required. But the typescript types shows it as required. Not really a bug, but it's quite inconvenient. Is there a way to walk around this until the next release?
export interface Options {
/** The start date of a recurring event's exception instance. Used for updating single event in a recurring series. */
exceptionDate: ISODateString;
/** iOS ONLY - If true the update will span all future events. If false it only update the single instance. */
futureEvents?: boolean;
}