A new report suggests that it was not the EU, but China, that helped "force" Apple to add support for RCS to the iPhone this year.
Obviously, it wasn't the EU
This makes sense because it was already leaked in October last year that the EU believes that Apple iMessage is not dominant enough in Europe to be labeled as a gatekeeper service, and is therefore not affected by the "Digital Markets Act" which comes into force on March 7. This was later officially confirmed on 13 February:
“And quite rightly: the EU has decided that iMessage does not fall under the DMA legislation because the service is not dominant enough. But that is not all they have decided today: Microsoft Bing, Edge, and the latter's marketing service also escape the strict regulations.”
Apple announced RCS support last November
It is John Gruber, a long-time Apple expert, who believes that it was already known in September that the EU was not going to force Apple to incorporate iMessage into the DMA legislation, and that it was therefore not the reason for Apple to go for RCS. The timing didn't make sense anyway, points out Gruber, who has another explanation: China. And when you understand what the Chinese authorities will impose in the country, it is not difficult to understand.
Chinese operators have been talking up RCS for many years, but last year they started the process of legislating that all new 5G mobiles must support RCS. The fact that the RCS protocol does not guarantee any kind of encryption is unsurprisingly unconcerned.