In addition to the schedule for automatically enabling/disabling the Always On Display on the Xiaomi smartphone, we can also set a permanent activation. Here, the Always On Display is always enabled when the device is in standby or sleep mode. In addition, we can also specify whether AoD should remain active during battery-saving mode.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Always-on display & Lock screen
Step 3:  Tap on  Show items
Step 4:  Tap on  Display items
Step 5:  Choose  Always
  1. Open the Settings
  2. Tap on Always-on display & Lock screen
  3. Tap on Show items
  4. Tap on Display items
  5. Choose Always

Xiaomi Instructions