Technically you appear offline to friends. It’s your clan you don’t appear offline to (correct me if I’m wrong.) Anyway, I can hear your request, so in the meantime simply choose “invite only,” and adjust your friends list, you don’t have to be friends with every clan member, and you don’t have to care if they see you online or not. Now there are players who play in clans only when they need them, then do their things when they don’t need them. One can assume this opportunistic approach to clan, or not. In any way shape or form, whether you appear online or not, you will not fool anyone. I prefer assuming my desire to play solo or not openly.