We offer our free WHOIS privacy service by default to many domain owners at the time of registration. We can only do that for domains from the registries that support WHOIS privacy, though. Some registries, mostly ccTLD ones, still just don't support it.
You can check the full list of the domain extension (TLDs) that do support WHOIS privacy.
Our WHOIS privacy service has always been available for those TLDs, and the service is added at registration for all TLDs that support it. It can be manually added in your dashboard by clicking on enable privacy for any domains that were registered prior to February 2017, or that didn't have it turned on for other reasons, e.g. transfer.
It can take a couple of days for WHOIS lookups to refresh their data and display the masking.
If WHOIS privacy isn't available for your domain name, this article has some good tips for other options: How To Create Your Own Whois Privacy Service.