Developer Psyonix confirmed how the new consoles (including Xbox Series S) will handle Rocket League in a post to the game's official site (opens in new tab). On top of the improvements available at launch, Psyonix is also planning to roll out an update that will let players choose between quality and performance modes sometime this year. As long as you have an Epic Games Account, all of your progress will come with you to your new console as well.
Here are the Rocket League next-gen upgrades broken down by console.
Rocket League PS5 upgrades
The Rocket League PS5 version supports 4K resolution with checkerboard rendering at 60 FPS and HDR.
Rocket League Xbox Series X upgrades
The Rocket League Xbox Series X version will support 4K resolution at 60 FPS with HDR at launch. Later this year, an update will add a new "Video Quality" setting to the game that will let you choose between two options: Quality, which runs at 4K resolution with HDR at 60 FPS; and Performance, which runs at 2688x1512 resolution - 70% of full 4K - with HDR at 120 FPS.
Rocket League Xbox Series S upgrades
The Rocket League Xbox Series S version will support 1080p resolution at 60 FPS with HDR at launch. Just like the Xbox Series X version, it will receive an update later this year to add two visual settings: Quality, which is 1080p / 60 FPS / HDR; and Performance, which is 1344x756 resolution / 120 FPS / HDR.