The Slip Space engine that Halo: Infinite uses was not entirely built from scratch. It still has foundation code from the old Blam engine that Halo uses. So it was more of a rework if anything and will still have some limitations the old engine had.
I believe this may be the main reason why 343 Industries are having issues graphicalyl for the open world aspect. And thus why it looks like late Xbox 360 graphics in some instances.
Source at timestamp 15:20 of this below video:
https://youtu.be/Dhg45VQfYWE<!–/data/user/0/com.samsung.android.app.notes/files/clipdata/clipdata_200730_164431_839.sdoc–>