I replayed it on Xbox series S and I can say the 20 Year Celebration works perfectly and flawlessly. i enjoyed better frame rate and better graphics. The first time I played it, it was years ago, 2015 or so and I played it on my XBOX 360 and I didn't enjoy it because of the frame rate. I recalled the story as it progressed and it is as good as I remembered. The game has some RPG elements: you can upgrade your gear and weaponry and also unlock new outfits. The 20 Year Celebration has some improvements and Baba Yaga story. I really enjoyed the Baba Yaga 2 hour branch of the story. You have to climb a lot, you shoot a lot and kill many, many enemies and the end of the game has a cliffhanger preparing you for the Shadow of the Tomb Raider.
What can I say more? It's a gorgeous game and every gamer should give it a try.