During a call, notifications can be received on the Samsung device and alarms are not muted during this time.

In the phone settings, we can disable (or enable) the Notify during calls feature, which will mute all notifications and alarms. Notifications are only heard after a call has been received.

Android 10 (One UI 2.0)
Step 1:  Open the  Phone-App
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Tap on  Call alerts and ringtones
Step 5:  Enable or disable  Notify during calls
  1. Open the Phone-App
  2. Open the menu
  3. Open the Settings
  4. Tap on Call alerts and ringtones
  5. Enable or disable Notify during calls

Samsung Instructions