Huawei made Harmony OS smartphones in 2 years. That said, they were uniquely motivated by the Google Mobile Services ban, Chinese state support, and likely had set the groundworks for such a transition much earlier.
> Reports surrounding an in-house operating system being developed by Huawei date back as far as 2012 in R&D stages with HarmonyOS NEXT system stack going back as early as 2015.
It wasn't green field to release in two years and likely had almost a decade of prep. It probably got additional resources with the Google Mobile Services ban... but even without that it would likely have shown up within the next few years.
In practice some apps run fine, but many are degraded or not running at all due to dependency on Google Play services, "security checks" and DRMs.