Xiaomi uses a proprietary charging protocol, I believe it is called Hypercharge. It also requires a proprietary cable with an extra pin/chip.

Looks like they opened the protocol, https://new.c.mi.com/global/post/1895204

Also, it's only for fast charging, you can use any other charger or wire without an issue.

You can charge it just fine with regular usb-c charger. So not a problem.