The game on PS5 will run at 1080p, 60 FPS, which is upscaled to a dynamic 4K resolution. This upscaling is due to technical issues with the game and will not be native at launch. Xbox Series X does get native 4K at 60 FPS, however.
At the end of the press release we received, the team do seem to be teasing a native next-gen port for Biomutant with them saying “It [the PS4 version of the game] will not be a native current-gen experience. More information on that will follow soon, though.”
So, expect to hear something later this year about a PS5 version of the game, or at least an update properly optimising the game for PS5. PS4 and PS4 Pro’s performance was revealed last week
Biomutant releases for PS4 on May 25, 2021, and is playable on PS5 via backwards compatibility.