By default numbers not in your contacts are blocked.

Optionally allow:

Numbers you have contacted
Numbers within the selected groups (Toll-Free, Local)
N registered call from the same number within T minutes
Numbers from messages
Numbers passing STIR verification (Android 11)

Contacted, Groups, Repeated, Messages options and the main toggle have additional settings. You can open them by long click.

If the app rejects calls from contacts on Android 10, allow contacts permi