Nothing Phone builds a blue bubble iMessage bridge while Google and Apple fight over RCS
(www.androidcentral.com)
In a video from MKBHD they mentioned this problem and they said that the idea is basically that Apple will not block it because it will bring them bad PR and attention from regulators who are concerned with anti trust issues. Hard to predict what will actually happen but Apple just blocking 3rd party access and citing (legitimate) privacy and security concerns seems to be a likely outcome.