Yes, the additional content DLC which is also included in the director's cut is. Unfortunately the changes they made to the base game in the director's cut are not available as an upgrade/DLC though.
The dlcs are available to purchase on the Xbox store.
FPS boost available on xbox series x
If I remember right, the Devs outsourced them to an outside studio to make, so they ended up where you had to fight them with guns etc, but as someone who leveled up heavy in stealth, this made them a huge pain to deal with. The directors cut reworked the boss fights, and allowed options to deal with them no matter your build. Does not outright ruin the game or anything though. Just annoying. I forget it you can change difficulty mid game, but if so I'll definitely drop it to easy on my replay just to get past them. Unfortunately not. At least for this console version. Didn't look into of you can on PC. The directors cut is also not available digitally. So you would need to track down a physical copy.
Absolutely love this game.