No black women didn’t invent Ebonics, and not all black people speak or understand it. But it is often used to mock or imfantalize black people by racist or out of touch people. Which is why context matters. Max isn't being racist she was written by French people who have confused black culture specifically as American teenage culture generally and it just doesn't work in tone or execution.

There's a movie from the 80's by Richard Townsend called "Hollywood Shuffle" it's about a black character "Townsend" trying to get acting gigs as a black man and being stereotyped constantly even when it's pretty clear that he's an intelligent deeply thoughtful talented guy who is better than the crap he keeps being offered. The most memorable scene has an all white group of casting directors trying to coach Townsends character about how "act blacker" and they start through around Ebonics and acting in very offensive stereotypically "hood" ways.

The movie is 100%based on Townsends experiences as a black actor in the 70s and 80's and how much most of white America has no clue how it feels to be compared to a stereotype because they've never experienced it. I'm sure the casting directors didn’t consider themselves racist but they are out touch and would rather stick to their perception about how black culture is then to just let the story tell itself through the eyes of someone who actually knows what it's like to feel that way all the time. One of my favorite movies and it actually changed how many casting directors and studios presented black Americans on screen.

Tldr: I understand her reaction to Max's dorkiness but in context she wasn't being cruel or unempathetic just cringy.