Most privacy advice assumes an attacker. Somebody intercepts traffic, breaks into a database, guesses a password. Encryption is the answer to those.
The leaks that actually happen in households rarely involve an attacker at all. Somebody takes a screenshot to remember a date. Somebody shares their screen during a video call. A phone is handed to a child who swipes through whatever is open. A laptop is mirrored to a television with the calendar still on screen.
In each case nobody decrypted anything they should not have. A copy simply exists, made by a person doing something ordinary.
The tab title is part of the leak
This one is under-appreciated. Every browser tab and application window has a title, and that title reaches further than the person sitting in front of it. Screen-sharing tools transmit the title along with the picture, and often list it in the window picker before the share begins. Screenshot utilities capture it when the whole screen is grabbed. The operating system keeps a list of open windows, which is how the app switcher works. Window titles also turn up in session restore, in crash reports and in browser history.
So a calendar named "Divorce lawyer" can leak through a tab while its contents remain perfectly encrypted. The same applies to a clinic name, a school, a rehabilitation programme, or the name of a support service. It makes no difference that the visible week is blank and every event inside it is ciphertext. The name sits on the outside of the envelope, and the outside is the part everyone can read.
Whatever you type into a calendar name is visible to anyone who ever sees your screen, including a stranger on the other end of a support call.
Previews, clipboards and shared albums
Notifications are a second channel. A lock screen that shows an event title shows it to whoever is holding the phone and to whoever is standing nearby. If a notification email quotes the event, anybody with access to that inbox sees it, including a shared family inbox or an account that syncs onto several devices.
CamyCal's server cannot read event titles, but it can see that one member tagged another, because it sends the notification email. That record holds an opaque identifier rather than a title, so the message does not quote the event. It is a deliberately narrow exception, and worth knowing about rather than assuming nothing at all is visible.
Clipboards travel further than people expect. Copying an event title on a phone can place it on a clipboard shared across that person's other devices, and clipboard history tools keep a list that outlives the copy.
Shared photo libraries are the third channel. A screenshot saved into a shared album syncs to everyone in that album, and albums frequently include screenshots by default. A booking confirmation, a school timetable, a letter about an appointment: each one becomes part of a collection other people can browse at leisure.
What to change in your own setup
Name things for the glance, not for the detail. "Appointment 3pm" means the same thing to the two people who need it and nothing to anyone who sees the tab. The specifics belong in the encrypted note, which is not rendered in a notification or a window title.
Check what your lock screen displays, and turn previews off for the calendar app if the answer is more than you want to show. Look at what a shared album syncs, because if it includes screenshots, it includes every screenshot. Treat screen sharing as publishing the whole screen: close the calendar tab first, or keep the sensitive ones in a separate window you can minimise.
Removing someone stops their access from that point on, but nothing recalls a copy they already downloaded or photographed. The decisions that hold are the ones made before the invitation.