I don't feel very concerned... That's kind of the point of the service.
Good that there's an opt-out.
edit: I dug around for it. They seem to mean the literal "Apps" settings page and not the "Settings" page. Every individual app that Gemini is capable of connecting to has a switch there. In Gemini, press your profile picture, then apps. In there you can both access the activity setting and decide which apps Gemini has access to.