I don't think there's any way that russia lost 300k troops but I could be wrong... Then again it's CNN so they are never going to follow up and do their own research, they are part of the propaganda arm of the US.
It's a cope, the funny part is that BBC set up a project to track Russian losses based on publicly available evidence, such as funerals, social media posts, etc. This is the only western count that has any methodology behind it, and it comes up with around 38k in losses. So, even if they're under counting, we could assume around 50k, that's still vastly below the wild numbers other western media keeps quoting.