To my knowledge, twitter doesn't block anyone from using slurs to begin with. I'm sure you can find plenty used on daily basis on "black twitter" for example.
That being said I'm going to need a more credible source than a random screenshot
Are you sure? Last time I checked it just gives you a pop-up asking if you're sure you want to use that word as some people can find it problematic and if you say yes it'll get posted like a normal tweet.