Solution:
The current WiFi 6 protocol is only available on a small number of phones.
For example: Mi 11, Mi 10, Mi 10Pro, iPhone11 full series (iPhone11, iPhone11 Pro, iPhone11 Pro Max), etc.
Note 1: Refer to the product parameter page for details about whether the mobile phone supports the WiFi 6 protocol. To use the WiFi 6 protocol, the terminal (such as the mobile phone) and router must support it at the same time.
Note 2: Mi Router AX9000 also supports 802.11 a/b/g/n/ac. Devices that don't support WiFi 6 can also connect to routers through other protocols.