Google has extended RCS with proprietary extensions [1] including E2EE. So there is plain RCS and Google RCS. https://www.theverge.com/2023/11/30/23981350/goo

Google has extended RCS with proprietary extensions [1] including E2EE. So there is plain RCS and Google RCS. https://www.theverge.com/2023/11/30/23981350/google-messages-chat-rcs-apple-imessage-photo-emoji https://www.theverge.com/2023/11/30/23981350/google-messages...