No, the phone variant of HarmonyOS runs on top of a Linux kernel.

...if there is will, a nice state sponsor and an already existing effective infrastructure.

Europe has none of the 3.

Can it run all of the kinds of apps that people (in the EU/US markets, which is relevant to the discussion at hand) actually want to run? SalifishOS doesn't even do that, at least not for me.

The will to create an OS is 0.0001% of the problem. There are tens of thousands of applications that people need to use that exist only for iPhone and Android.

There are dozens of functional mobile OSes. And OS isn’t useful unless it has application support for the tasks people want to accomplish, though.

I think it's more of an EU problem. We have so many public apps that rely on two big American tech companies solely because the EU has yet to figure out an alternative app store with enough security to make those apps available. This likely made sense 10 years ago, but today with all the talk about digital sovereignty it's frankly a little weak. It's not the OS that is the issue though, I could use graphene or similar just fine, but they wouldn't let me run a single of the apps that are the sole reason I have a smartphone. Well.. maybe the Microsoft authenticator?

I mean, I have to write exit strategies from Azure because the EU might demand our industry to leave non-EU infra. Yet ironically the digital company ID I would need to sign new contracts with within Europe aren't available without one of the two app stores. It's not that I can't sign those contracts without the ID, but I'd probably have to go to Germany in person.

Access to the Play Store requires the proprietary Google Play Services code, so I doubt this has it. The alternative would be installing apps via APK files.