If automatic downloading of updates is enabled on the Xiaomi device, we can turn on/off whether or not to use mobile data for this purpose. If this
feature is disabled, updates are downloaded exclusively over a wireless network. If downloading over mobile data is enabled, we can set a schedule for the auto updates.

Note: We recommend disabling this feature and downloading updates over a wireless network only to maintain control over the data volume.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  About phone
Step 3:  Tap on  MIUI version
Step 4:  Open the  menu
Step 5:  Tap on  Update settings
Step 6:  Enable or disable  Download using mobile data
  1. Open the Settings
  2. Tap on About phone
  3. Tap on MIUI version
  4. Open the menu
  5. Tap on Update settings
  6. Enable or disable Download using mobile data

Xiaomi Instructions