This is what I call a false biopic. These are usually extremely well made movies with good production values, well acted and directed but they also play fast and loose with the actual facts as to make them more "interesting" to the audience. This genre is very popular, especially in the UK, as they are good award bait and popular with the audiences. These are usually never bad movies and I can't really give them a bad rating, but they also almost always leave me a bit flat and, to be honest, I am getting a bit tired of them. So, Red Joan falls in this category and I have nothing more to add about it, except that at least the creators, having changed almost everything regarding the true story, gave us the courtesy of changing the name of the titular character, a move which I think is at least a bit more honest.
