How to block calls from unidentified numbers on Android phones

We all get multiple phone calls every day and there may be times when a majority of calls that we receive are either spam or from unidentified numbers. These calls may be from telemarketers, spammers, or scammers who use automated systems to make unsolicited calls to a large number of phone numbers. While we have apps, such as Truecaller, that can identify numbers for us, it would be better if we can block such calls.

In some cases, we also get calls from individuals or businesses that have blocked their phone numbers for privacy reasons or to prevent their number from being identified.