Making an attendee optional only affects how they appear on the event invite and does not affect how Xena looks for available times.
As a workaround, ask Xena to schedule your event with the highest-priority attendees first and then add your optional attendees in a second message.
๐ง Reminder: You can always ask Xena to offer options before scheduling.
Schedule with a mandatory and an optional attendee:
Say something like "Schedule 15 minutes in January for a Q1 check in with @Melissa Armstrong and include @Sarah Spingler as optional."
Schedule with a mandatory attendee then add an optional attendee:
Say something like "Schedule a catch up with @Sarah Spingler." Once Xena schedules your event, reply in the thread with something like "Add @Mark Noskoff as optional."