No they are not. Google uses a proprietary extension to RCS to support end to end encryption that iOS doesn't support.
GSMA added end to end encryption using MLS to the RCS universal profile in March. For one to one messages the latest betas of Google Messages contain a flag to enable MLS support. It is expected Google will add the support for group messages and enable MLS by default sometime soon. Apple has committed to supporting MLS in a future update. So eventually there will be end to end encryption between the two ecosystems.