Once the Xiaomi smartphone has successfully connected to a wireless network, the connection is restored by default when the device is again within range of that wireless network, but we can disable this feature for each individual network if desired.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Wi-Fi
Step 3:  Open the  networks settings
Step 4:  Enable or disable  Auto connect
Step 5:  Tap on  Save
  1. Open the Settings
  2. Tap on Wi-Fi
  3. Open the networks settings
  4. Enable or disable Auto connect
  5. Tap on Save

Xiaomi Instructions