I think you need to look up where rcs came from and why it was the adopted standard agreed to by most everyone, because Google had pretty much jack all to do with it.
I think you need to look up how it is actually implemented in the wild today, because Google extended it and a very large number of people are using Google Jibe.
It worked out well for Microsoft since Apple dropped their lawsuit over QuickTime code that made it into Windows via an Intel contractor.
RCS is in iOS 18, but “integrate the messaging system compatibility” really means “use Google’s RCS”.
I think you need to look up where rcs came from and why it was the adopted standard agreed to by most everyone, because Google had pretty much jack all to do with it.
I think you need to look up how it is actually implemented in the wild today, because Google extended it and a very large number of people are using Google Jibe.