Gmail: Click the gear icon in the top right of Gmail > See All Settings. From there, turn off Smart Compose, Smart Compose Personalization, and Smart Reply. (There’s also the Smart Features setting, which turns off everything even remotely AI-related, but that will also disable spelling and grammar check.)

On device: Open the Gemini app on your Android. Tap your profile icon in the top-right corner. Go to Gemini Apps Activity. Tap Turn off Turn off and delete activity, and follow the prompts. Select your profile icon again and go to Apps. Tap the toggle switch to prevent Gemini from interacting with Google apps and third-party services. Avoid using Gemini Deep Research with Gmail, Drive, or Chat (these sources are turned off by default). If you have already selected them when enabling Deep Research, open Sources* and clear their checkboxes.

Once that's done, disable the app or remove it if your device allows that.