Kamala talking like she was a southern black person in order to appeal to black voters was some dumb shit.
She doesn't need to pretend to be black to appeal black voters. She is black.
Secondly, black people all over the country say y'all (not just southern black people). That's because the origin of black culture in America is southern and second generation black Americans assimilate into the larger black American culture in the same ways a second generation white American would assimilate.
And lastly, almost all educated black people code switch. That might seem weird to you but it doesn't to black people.