Why your free slots show as Busy

Check Show real availability in the sync's Appearance settings. When it's on, a copy carries the same free-or-busy status as the original, so an event marked Free stays Free. When it's off, copies land as Busy, because Busy is what every calendar provider gives a new event by default.

New syncs have this on. If yours is off, it's either a sync you made before the default changed, or it got turned off at some point.

The setting people usually mean instead

Two settings sound like they do the same thing. They don't.

Title says "Busy" changes the name. It replaces the event's title with the word "Busy" so nobody reading your calendar sees what the meeting actually is. The slot is still blocked either way.

Show real availability changes the free-or-busy status: whether the slot blocks your time at all, and whether scheduling tools consider you available.

If your problem is "my colleagues can see my dentist appointment", you want the title setting. If your problem is "I marked this Free but it's still blocking my day", you want Show real availability. Masking the title does nothing for the second one, which is where the confusion usually starts.

If Show real availability is already on and slots still show Busy

Check the original event. Google, Outlook and iCloud all default new events to Busy, so an event you assumed was Free may never have been marked Free in the first place. Open it on the source calendar and look at its own free/busy setting.

If the original really is Free, the copy was probably written before you turned the setting on. Existing copies aren't rewritten the moment you save a setting — they update on the next run. To push the change through now, open the sync's menu and choose Re-sync.

Two cases that are working as intended even though they look wrong:

• All-day events. Most calendar apps show all-day events as Free by default and draw them in a banner at the top rather than blocking hours. If a copy blocks the whole day, check whether the original was actually all-day or just a long timed event.
• Declined and unanswered invitations. Those are governed by the sync's accepted/tentative filter, not by availability. If unwanted invitations are blocking your time, that filter is the setting to change.

Known limitations

• Show real availability applies to a whole sync, unless you're on Pro, where you can set it per destination calendar under Calendar exceptions.
• Turning it off again resets copies to Busy rather than leaving them as they were. Off means "everything lands as Busy", not "stop managing this".
• Only two states cross between providers, Free and Busy. Outlook's finer settings (Tentative, Working elsewhere, Out of office) arrive as one or the other. Nothing carries the exact original label.