GrapheneOS?
As far as I can tell by skimming Wikipedia, no. Its based on something called OpenHarmony, which itself was based on something called LiteOS Source: https://en.m.wikipedia.org/wiki/OpenHarmony
Edit: Looks like HarmonyOS used to be based off of Android, but has transitioned to OpenHarmony extremely recently. “It replaces the OpenHarmony multi-kernel system with its own HarmonyOS microkernel at its core, removes all Android code and supports only apps in its native App format.” https://en.m.wikipedia.org/wiki/HarmonyOS
So while you would’ve been correct a few months ago, it appears this is no longer the case. I can see why my comment would’ve seemed stupid at first.
aint harmonyos also android derivative?
Read the article before commenting guesses