From this article:
https://www.caranddriver.com/bmw/x7-2021
The xDrive40i's powertrain gets a 48-volt starter-generator which, surprisingly, worsens its EPA fuel-economy figures; both its city and highway ratings drop by 1 mpg. The X7 also adds a handful of newly standard features, including long-overdue Android Auto compatibility. The previously available Off-Road package, which brought an electronic limited-slip rear differential and underbody protection, is no longer offered.
I have a 2021 X7 40i, so let me know if you have any questions.