The functions of the Contacts app on the Xiaomi device are simplified and adequately described.
Contacts can be exported as a VCF file to the SIM card or phone memory / internal storage.
From there, the exported contacts can be sent to other devices.
Also, the function only allows exporting all contacts. To export selected contacts, the Xiaomi smartphone's Share function must be used.

Android 10 (MIUI 12.0)
Step 1:  Open the  Contacts app
Step 2:  Open the  menu
Step 3:  Tap on  Import/Export contacts
Step 4:  Choose  Export to storage  or  Export to SIM card 1 / 2
Step 5:  Tap on  OK
  1. Open the Contacts app
  2. Open the menu
  3. Tap on Import/Export contacts
  4. Choose Export to storage or Export to SIM card 1 / 2
  5. Tap on OK

Xiaomi Instructions