I see your point. But I do not see this part of the scope of GrapheneOS. Install a text launcher, so they are annoeyed. Or put an other icon on top of your private messages app. This is no OS level security what you want. I simpy say, that whatever you request probably already exists. Use a second profile and show this profile to them. Only in your head having nothing is suspicious. Why is it not plausible, that you bought your phone today? This definitly is plausible. Graphene can not solve social engineering problems. The can deliver good technical solutions to real problems.