When we enter a phone number via the dial keypad in the Xiaomi smartphone's phone app, a short tone sounds with each digit entered, which can be (de)activated according to personal preference.

Android 10 (MIUI 12.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Sound & vibration
Step 3:  Tap on  Additional settings
Step 4:  Enable or disable  Dial pad tones
  1. Open the Settings
  2. Tap on Sound & vibration
  3. Tap on Additional settings
  4. Enable or disable Dial pad tones

Xiaomi Instructions