Our own phone number is transmitted or sent to the caller by default. The Xiaomi smartphone uses the operator's default network setting for this. If desired, we can hide the phone number.
This setting is saved on the SIM card.

Android 10 (MIUI 12.0)
Step 1:  Open the  Phone app
Step 2:  Open the  Settings
Step 3:  Tap on  Advanced settings
Step 4:  Tap on  Caller ID
Step 5:  Choose a  SIM card   (Dual SIM)
Step 6:  Tap on  Caller ID
Step 7:  Choose  Network default ,  Hide number  or  Show number
  1. Open the Phone app
  2. Open the Settings
  3. Tap on Advanced settings
  4. Tap on Caller ID
  5. Choose a SIM card (Dual SIM)
  6. Tap on Caller ID
  7. Choose Network default, Hide number or Show number

Xiaomi Instructions