Book a room without a meeting, becomes visible:

Update: Think I've found it - in the OnVisible property of the meeting select screen there is:
ClearCollect(FutureCalendarEvents,
Filter(
Office365.GetEventsCalendarViewV2(MyCalendar, Text(DateAdd(DateSelected, -1, Hours), UTC), Text(DateAdd(DateSelected, 1, Days), UTC)).value,
Organizer=MyName.Mail
)
It looks like its filtering out meetings that weren't created by me.
Changed it to :
ClearCollect(FutureCalendarEvents,
Office365.GetEventsCalendarViewV2(MyCalendar, Text(DateAdd(DateSelected, -1, Hours), UTC), Text(DateAdd(DateSelected, 1, Days), UTC)).value);
and all seems to be well 🙂