Hello @Ken21, @Branka-and-Silvia0,
The calendar settings page has been changed.
I'm not sure if the new setting applies in all countries.
The setting "host/manage listings/calendar and more/availability settings/reservation preferences/minimum stay/" doesn't exist any more in the new arrangement.
You can go to "Host", then "Calendar", then "Manage settings" in the top right. Then click "Availability" and then click "Edit" in the "Trip length" section. Then click "Add a requirement for seasons or weekends" and select your season or dates from the drop down "Duration" list.