On Google Calendar as well as Fastmail Calendar there are options to create a share link for your calendar which only exposes availability but not any details of the events other than date/time/duration. It’s not granular other than that though. I use it to share my personal calendar with my work so I can e.g. schedule a doctor appointment with details and have that appear and affect availability in my work calendar - it just shows up as “Unavailable” with no other details.