Every SIM card comes with a PIN lock as standard to prevent unauthorized access, so when we start the Xiaomi smartphone, we are first asked for the PIN and then for the unlock pattern or code. If this is too much code entry, you can deactivate the SIM PIN lock if you wish.

Note: If the SIM lock is deactivated, the SIM card is unprotected, which means that if you put the SIM into another smartphone, you have immediate access to all SIM applications and services.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Passwords & security
Step 3:  Tap on  Privacy
Step 4:  Choose a  SIM card   (Dual SIM)
Step 5:  Enable or disable  Lock SIM card
Step 6:  Enter the current  PIN  and tap  OK
  1. Open the Settings
  2. Tap on Passwords & security
  3. Tap on Privacy
  4. Choose a SIM card (Dual SIM)
  5. Enable or disable Lock SIM card
  6. Enter the current PIN and tap OK

Xiaomi Instructions