We can adjust the ringtone of the Xiaomi smartphone. the ringtone is set as default and will be played for incoming calls.
if no other ringtone is set in other apps that support video telephony, for example, the selected default ringtone will be played. If we use the dual-SIM function, we can set or specify the ringtone for calls on the respective SIM card individually.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Sound & vibration
Step 3:  Tap on  Ringtone
Step 4:  Choose a  SIM card   (Dual SIM)
Step 5:  Tap on  All ringtones
Step 6:  Choose a  ringtone
  1. Open the Settings
  2. Tap on Sound & vibration
  3. Tap on Ringtone
  4. Choose a SIM card (Dual SIM)
  5. Tap on All ringtones
  6. Choose a ringtone

Xiaomi Instructions