Does Thendoo change my Google Calendar?

No. Thendoo only reads your Google calendars: the list of calendars and their events. It doesn’t add, move or delete anything in them.

There’s one optional exception you control. If you turn on Show my time blocks in Google Calendar, Thendoo creates a separate calendar called “Thendoo” in your Google account and puts your planned time blocks there. That way colleagues see you as busy, and you see your plan on your phone’s calendar. Your other calendars are never touched, and Google only lets Thendoo manage the calendar it created.

Thendoo asks Google for the narrowest permission it needs, and asks for more only when you first use a feature that needs it.

Editing your own Google events from Thendoo and creating Google Meet links are planned. When they arrive, Thendoo will ask for that permission at the moment you first use them, never before.