It's generally there, but for some reason the game only limits the screen size against the left and top edges in the new version. Guessing it has to do with how they are getting the game to show 4:3 instead of 16:9. But generally speaking make sure you don't touch the cursor at all while the game is starting. Once it's started move the cursor toward the top / left of the screen and it will usually show up on screen.
You can clearly tell there is additional screen real estate, as you move the mouse off screen it takes the same amount of movement to get it back on screen. So at 4K you can likely move it a huge amount off screen.