Only Google’s proprietary extension has encryption. The actual industry standard specification of RCS has no encryption defined at all.

Edit: It turns out Apple have refused to use Google’s proprietary encryption implementation and are instead working with GSMA to update the RCS Universal Profile specification to finally have encryption defined and standardised so that any RCS client can handle encrypted payloads (whereas only Google Messages today can do encrypted RCS and requires other users to be exclusively using Google Messages otherwise messages are sent unencrypted).