At Apple, we build our products and services with industry-leading privacy and security technologies designed to give users control of their data and keep personal information safe. We took steps to protect our users by blocking techniques that exploit fake credentials in order to gain access to iMessage. These techniques posed significant risks to user security and privacy, including the potential for metadata exposure and enabling unwanted messages, spam, and phishing attacks. We will continue to make updates in the future to protect our users.
Note that RCS as a standard doesn’t include End-To-End-Encryption because the telcom companies which designed it could not introduce that as per US law. Google added End-To-End-Encryption with Google Messages.