Sorry to be a bringer of bad news, but I don’t think that RCS messaging is going to work without full GAPPS, and even then it may also need root to do some things. But with iodéOS and microG I don’t think we will have success. This microG issue thread marked RCS support as “Not Planned”.
With RCS not being a secure as advertised, and with the bugginess of it, and the interoperability questions with Apple, and the locked down to only use Google Messages, etc. I really hope that the world (well, the USA in my case) will not embrace it and will finally move to more secure universal messaging like Signal as default. But I don’t think that will happen either 