When the timer expires, the timer tone sounds, and if that is not enough for us, we can also activate the vibration.

Android 10 (One UI 2.0)
Step 1:  Open the  Clock -App
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Enable or disable  Vibration
  1. Open the Clock-App
  2. Open the menu
  3. Open the Settings
  4. Enable or disable Vibration

Samsung Instructions