It has it in its current documentation (maybe 3.0 too? I forget, but it's new this year), and Apple and Google have had messages to themselves encrypted for a while (but not to each other, which is what the RCS docs are intended to resolve). It took many years to get it documented though (despite loudly claiming RCS is more secure the whole time), and AFAIK none yet implement it. Definitely none with all the documented things it needs to show to be compliant with the spec I read, e.g. key verification - I certainly don't see any of that in Google's "Messages" app! Though hopefully that will all change.

But honestly, in a non-open ecosystem, can you really trust that the near-exclusive two major players are actually playing by the rules? Apple has been relatively protective of its users on privacy stuff, but I've lost all trust in Google at this point.