Developer: Game Freak
The Teal Mask is the first of 2 expansions for Pokemon Scarlet and Violet included in The Hidden Treasure of Area Zero DLC bundle. It adds new story content, a new area, and 110 Pokemon to the game. If you were looking for performance fixes; though, you won't find many here.
Let's get this out of the way; this patch does not fix the framerate. In fact, it doesn't fix anything about the graphics. The framerate is still bad in the old areas, and it's just as bad in the new areas. Shadows still flicker, NPCs and Pokemon still drop to 2 frames per second when they're more than 10 ft away from you, and you can still see the LOD deforming mountains as you run around. The only thing that has gotten a noticeable improvement is the Pokemon PC boxes, which now load almost instantly. The boxes were very annoying because they didn't load custom wallpapers until you did something in the box and took like 5 seconds to start loading the Pokemon icons, so this is a great improvement, but it's probably not the fix most people were hoping for. Frankly, I don't think they're ever going to fix the framerate unless the next Nintendo system can somehow do it itself. The developers still working on this game are just making content.
The Teal Mask takes place in a completely new area called, The Land of Kitakami. They don't call it a new "region", like Paldea. I think it's only a little bigger than the Crown Tundra. It's a mountainous area surrounded by forests, so it doesn't look like it's the area North East of Paldea, but you take a bus there, so I guess it must be close. The area North East of Paldea still isn't filled in, by the way. Kitakami as a new place to run around in is pretty cool. I love the rural Japanese theme with the rice paddies, forests, and shrines, and the new music is really good. This is where I'll go when I want to do some raids now.