What's the one privacy setting almost everyone forgets to check?

Trying to crowdsource a list here, so bear with me.

Every app or service has that one buried privacy setting that's on by default and almost nobody finds it on their own. Things like ad personalization, location history, who can see your "last seen" status, or background app data sharing.

What's the one you always tell people to turn off first when you're helping a friend or family member lock down their accounts?

Would love real examples here, not just "check your privacy settings" in general 🙂