In modern world new mobile OS for usual client (B2C) will not be created without government support. OS is platform and you need to have native apps of popular services. Possibility to run native apps from other OS will not work for adoption. I know only 2 cases in modern world - HarmonyOS and Aurora OS. Both created from special requests.

Microsoft closed WIndows Phone becasuse it can't be popular without Google services, especially YouTube. Google didn't create native apps and this is way of destroying other mobile OSs