In Blindspotting (2018), a white protagonist is shown as being able to fluently speak an incomprehensibly dense version of AAVE, and it’s revealed later he has no idea what he’s saying (despite communicating effectively). I’ve never seen anyone criticize that joke.
The joke is how incongruous it is that she speaks their language despite being very white. It only works because you expect black people to speak like black people and white people to speak like white people.
Sure, the old white woman using heavy black slang is where the joke comes in.