Hi @Mara1363
@Mike-And-Jane0 found the easiest way to do this is by turning on Pro Tools and using the multicalendar (not the regular calendar) to block future dates. I re-posted their solution below:
Thank you! I think you found the answer for sure! Looks like the ability to block dates past a 3 month window (or any availability; 6mos, 9mos 12mos) are only available if you have Pro Tools turned on and use the multicalendar to block dates past your window (you can't use the standard calendar). I just checked this morning. The standard view calendar does not have that option any longer for any dates past our booking window of 12 months (not sure if it works that way for "all future dates, but not sure many would be using that).
Since all Hosts can use Pro Tools now (used to be only if you had 6 or more listings), that appears to be the solution for everyone now. Even if you only use Pro Tools and the multicalendar to accomplish blocking dates past your window, it would be a real time-saver and definitely worth doing it.
How to Use Pro Tools, Rule Sets & Multicalendar
https://community.withairbnb.com/t5/Community-Guides/GUIDE-Use-Pro-Tools-to-Set-Calendar-Custom-Pric...
With Pro Tools you have the option to block a future date on your multicalendar. The regular calendar doesn't offer that option if the date is outside your booking window....the multicalendar does.

Hope this helps. Let us know here if it works for you.