So I did some reading on the whole Ciri thing out of curiosity, and I'm starting to understand the more in-depth reasons that are even making a lot of reasonable people upset. In the posts above you basically just said you were mad because she has to meet your aesthetic standards and you don't like black women, which to me is not something I agree with and it sounded like a shallow argument.
I'm not far enough into the Witcher games (just started 2) to know anything so I figured I'd do a little research. As I read the story implications and how it would have to radically change her entire lineage and therefore the regions, history and bloodlines of her character, I can understand why people (especially Polish, on which the mythology is based) feel like they are seriously fucking with the novels/games. It would also screw up the dynamics between Ciri and Geralt's characters since a lot of that relationship grows from people believing she is Geralt's daughter due to how similar they look. Added to that, it does indeed seem to be confirmed that they basically said no Caucasian's would be allowed in the casting call, for a character that more than most, should be white.
I know the whole "would you cast a white guy as Shaft" or "make the Black Panther white", argument is a bit on the nose and kind of a political talking point now, but it is a fairly accurate example. If a character's heritage is an important key to that character, and one of the most important pieces of lore would be completely turned upside down, you probably shouldn't make it a specific requirement to change that character too much.
So... Reluctantly. I agree it's a stupid choice. They could have easily made another Witcher or major character another race and most people would barely notice. But don't do a minority only casting call on a pivotal character that's designed to be ghostly pale. If the casting call turns out to be untrue fine, but Netflix is not denying it and copies of it are popping up everywhere.