The update adds a Preferred Mode option in the menu, which offers three different options: Resolution, Balanced and Framerate.
The first boosts the resolution ‘at the expense of image quality’. On Xbox Series X, the game runs in 4K at 60 frames per second, and on Xbox Series S at 1440p and 60 frames per second.
Balanced resolution down for better image quality. Thus, the game will run on both Xbox consoles in 1440p at sixty frames per second.
Finally, the Balanced mode makes it possible to play the game in 120 fps, on Series X in 1440p and on Series S in 1080p.
At the moment nothing is known about a similar update for PlayStation 5. According to Rocket League creator Psyonix has that for a technical reason.
“Adding 120Hz on Xbox Series X and S is a minor patch, but on PlayStation 5 it requires a full port due to how backwards compatiblity works on the console “, says the developer to Eurogamer.