Plus, unless they fixed it, if you enable RCS and then regret it and disable it again, anybody who texted with you via RCS will no longer be able to text you at all. Things won't revert to SMS.
This bit me pretty hard, but I finally fixed it by changing my phone number.
https://messages.google.com/disable-chat
This is similar to Apple's iMessage deregistration page.[1]
Google has been funneling RCS messages through its own servers to bypass wireless carriers, which were slow or unwilling to directly support RCS.[2] Unfortunately, this has centralized RCS communications through Google and allowed Google to make end-to-end encryption available to RCS users as a proprietary extension that Google never contributed back to the RCS Universal Profile specification.[3]
For RCS on Android to be decentralized again, your wireless carrier would need to support RCS on the network level and Android would also need to implement RCS in a way that does not require interaction with Google servers. This would make deregistration unnecessary.
[1] https://selfsolve.apple.com/deregister-imessage/
[2] https://www.extremetech.com/mobile/302020-google-will-bypass...
[3] https://appleinsider.com/articles/23/11/16/apples-flavor-of-...
(Ditto for Apple, if that's still an issue over there with iMessage as well.)
Frankly, I expect Google to fix their mistake before the telecom support people figure it out. It'll be a nightmarish headache for all involved.
On a relative's phone, the messages app simply enabled RCS automatically without asking (and displayed a screen proudly saying it did so). Does that means that this phone will never receive SMS again from RCS users, even though we have carefully always answered "no" when it asked whether it should enable RCS (and quickly disabled it again once it enabled automatically)?
This was quite a while ago. They may very well have fixed the issue since then.
And yes, I noticed they enable RCS by default. Since then, the first thing I have done with new phones is to disable RCS. If you do that before sending/receiving any texts, then there is no issue.
That same "bug" existed for years with iMessage, for anyone switching from an iPhone to a non-iPhone.
It still exists in some form, albeit less severely, because Apple finally implemented a timeout and a way to manually deregister a number, but it took years.