Smart features read message content. Gemini side panels add more.
Smart features read your messages. Gemini in Workspace is a separate switch again.
Gmail Settings, General tab.
Turn off both smart feature switches in Gmail settings, then check the Data and privacy page on your Google account for Gemini-related activity controls.
A managed Workspace account may have these locked by an administrator. If the switch is greyed out, mark it blocked rather than failed.
Smart features and Workspace Gemini are separate settings. Turning one off does not turn off the other.
Every service on that list buries its opt-out somewhere different. Don't Train On Me puts all of them in one checklist in a panel beside your browser, walks you through them one at a time, and helps you confirm your privacy settings on the ones that expose a setting it can read. Free, no account, and nothing you tick leaves your machine.