I personally find things like this a little irksome. Especially considering the backdrop of people who whine whenever a white person happens to take the place of a black character. Which ever way people feel about the issue, they should at least be consistent about it.
Although it also depends on the context. If Quintin Tarantino made a film and he cast a black actor to play an historical white figure, I'd be cool with that. His films are often tongue and cheek and not meant to be very formal. I'm not familiar with this series, but if it's going for an historical vibe... yeah this stuff kind of sticks out like a sore thumb. Just screams political to me. Like Hannibal being casted as a sub-Saharan African in historical documentaries. It's most likely meant to skew/rewrite history. The same is true in the reverse, I don't like historical Egyptian based films for instance where the cast is all white people, lol. I don't really care about the origin of the character. If makeup can make them look convincing, fair enough. For instance, a black person with mixed racial ancestry may be able to naturally pull off a Mediterranean look.
I didn't read the story; I don't really understand the grounds where they can sue. The only thing I can think of is that the Egyptian government helped finance this series and the director went behind their back to cast a black lady as Cleopatra. Like many others, I'm simply just going to scroll past it. I've heard it's gotten rotten reviews anyways.