Apple gets the message, RCS coming to iPhone in 2024 with same Universal Profile as Android

It's more likely Google has paid them.

There would have to be a court case and ruling before Apple could be threatened with a fine. For messaging this isn't the case (so far). Apple doesn't restrict access to messaging apps. You can install iMessage competitors.

The RCS apple is implementing is Google's standard. That they control and have restricted access to. So far only Google, Samsung and Apple have been allowed to use it.