If even Apple says iMessage isn’t used by at least 45 million EU citizens… (to qualify for gatekeeper status)
What do you mean? If Apple includes RCS like they did SMS then it would operate as follows:
Is target an iPhone with iMessage enabled? Yes? Use iMessage. No? Fallback to RCS. RCS doesn’t work? Fallback to SMS.
Even carriers that supported RCS, like Vodafone, have shut it down https://9to5google.com/2023/03/27/vodafone-rcs-messages-andr...
Apple won't make the iPhone fall back to sending RCS though Google servers (like Android does) if there isn't carrier support for it, they'll just say "there is no RCS support on your carrier" and go for SMS.
But I guess it was worth to try this instead of directly opening iMessage for interop, for business reasons.
The word "Mac" encompasses all of those, just fyi.