In the US, raising one finger means “Give me a minute”. It can be very helpful if you’re processing slowly or need some time to find works.
However, shaking a finger means “You’re doing something I don’t like, and I’m expressing contempt by treating you like a naughty child”.
So, it’s a signal that doesn’t work well if you can’t easily tell the difference between raising your finger and shaking your finger.
i usually raise my whole hand, but facing the other person sideways (not palm out like STOP which is too harsh for this context), fingers relaxed (or two fingers up, the others loosely curled). no finger-shaking or pointing required!