I do think this is a bit more nuanced than some of the faux wide-eyed responses are claiming.
There is clearly nothing wrong with a young white child choosing and playing with a black doll.
But for an adult to choose a black doll for a white child is a bit more complicated, because, unfortunately, the dominance of white dolls means that choosing a non-white doll is a deliberate choice. So this means it becomes a question of why the adult has chosen a black doll.
Perhaps its simply because the doll in question has cooler accessories, in which case all good.
Or perhaps it might be because the adult wants to normalise diversity, which is at least well-intentioned.
But it could be because the adult just wants an easy way (consciously or unconsciously) to signal to other adults just how right-on they are as parents, while not concerning themselves in any way with the real issues surrounding diversity and racism. Which while not cultural appropriation, is something not completely dissimilar.