Depending on the model, DNS may or may not be available on the Xiaomi smartphone. By default, the function is already set to "Automatic", but it can also be turned off. You can also use your own DNS server.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Connection & sharing
Step 3:  Tap on  Private DNS
Step 4:  Choose  Off ,  Automatic  or  Private DNS provider hostname
Step 5:  Tap on  Save
  1. Open the Settings
  2. Tap on Connection & sharing
  3. Tap on Private DNS
  4. Choose Off, Automatic or Private DNS provider hostname
  5. Tap on Save

Xiaomi Instructions