It is now. Boba Fett's armor used to be classified as durasteel, and you can look it up in most Star Wars Encyclopedia books. But recently, after seeing the success of the Mandalorian and not wanting to disrespect the original gangster, they retconned Boba Fett's armor to be beskar. They haven't detailed if it's pure beskar but seeing as it's colorful and full of scars, it probably isn't.