I did just manage to dig up a source that says these things are somewhat implemented in iOS 18 with illustrative screenshots rather than actuals, and it seems to be implemented but currently janky:

- On iOS, rich cards have a message length limit of 144 characters. (Implies this is not a limitation on Android.)

- On iOS, multi-CTA might fold some of the options away. So you might give 4 options and it renders 2 options and makes you use a drop-down for the others.

- On iOS, carousels display as cards, which might not be as obvious to interact with.

https://www.infobip.com/blog/apple-rcs

Potentially improved in iOS 26. It's a little hard to work out the state of this, and of course not trivial to test without joining some kind of partner ecosystem.