By default, all calls are muted in the Do Not Disturb mode of the Samsung device. If you still want to receive calls, you can allow this in the settings. In addition to all calls, only those that are saved as contacts or even marked as favourites can be allowed.

Available options:

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Notifications
Step 3:  Tap on  Do not disturb
Step 4:  Tap on  Allow exceptions
Step 5:  Tap on  Calls from
Step 6:  Choose between  All,   Contacts only ,  Favourite contacts only  and  None
  1. Open the Settings
  2. Tap on Notifications
  3. Tap on Do not disturb
  4. Tap on Allow exceptions
  5. Tap on Calls from
  6. Choose between All, Contacts only, Favourite contacts only and None

Samsung Instructions