Hi Brigitte,
Thank you, that worked. I think I see the problem here, it is a bit more complicated. What I didn’t assume, that a property can be occupied over multiple dates, so it is dependent on the date, and it cannot be stored within a single field. The calendars probably have a more complex data structure for that. The date filter in this case probably does nothing, as the availability cannot be determined by single field comparision.
May I ask, which plugin do you use to manage the availability? I might be able to suggest a simple custom code to exclude the results, if they have an API to check by dates. Otherwise this might be only possible to resolve via customization.