Share a whole calendar with "See only free/busy (hide details)" option

Is your feature request related to a problem? Please describe.

Being 100% telework, and telework allowing a certain flexibility with private life, I sometimes have personal constraints (appointments, travel, etc.). During these time slots, I would like people to know that I am not available, but how can I do it? Share my personal calendar and mark each event whose details I do not want to be visible? No, it's too tedious. Duplicate personal events to my professional calendar and indicate "not there" or "busy". I do it, but it's tedious, especially since sometimes I forget to do it.

Describe the solution you'd like

Currently, unless I missed a feature, if I want an event to be visible to another person without displaying its details, I have to specify it event by event (event visibility option), but this cannot be done by default retroactively and for any new event (directly applied to the entire calendar, in the sharing option).

Many years ago (maybe 10), when I was still using "Google Calendar" (sorry to say that, it's blasphemy), I saw that it was possible to share a calendar with another account by specifying "See only free/busy (hide details)".

This is IMO very useful — for example — for associates who share their professional calendar and their personal calendar. The professional calendar remains fully visible (all details), while the personal calendar simply indicates occupied time slots with a free or busy information. This avoids collisions when making appointments and allows the respect of the privacy of others.

Describe alternatives you've considered

No response

Additional context

No response

No files, tests, or entry points are named in the issue. Start by tracing the existing calendar-sharing and event-visibility settings, then determine how a calendar-level free/busy option should apply to existing and newly created events; done means shared viewers see occupied time slots without event details.