Why...? It's obviously a tool to spy on their citizens even more effectively and very possibly to spy on western citizens as well.
I'm all for alternatives to Android and iOS, but I'd rather be spied on by private companies than a country that pretty much plans to take over Asia and then the rest of the world in the coming decades (well, in my wet dreams SailfishOS matures as a real alternative and I don't have to choose Android at all).
There is some open core, but system you recieve in the end device is going to be totally locked and without source code to see.
The only component with available source will be Linux kernel, because of it's user-friendly copyleft licence, but it is so much modified even on Android it's basically useless.
Here's the summary for the wikipedia article you mentioned in your comment:
Red Star OS (Korean: 붉은별; MR: Pulgŭnbyŏl) is a North Korean Linux distribution, with development first starting in 1998 at the Korea Computer Center (KCC). Prior to its release, computers in North Korea typically used Red Hat Linux, and later switched to modified versions of Microsoft Windows with North Korean language packs installed. Version 3. 0 was released in the summer of 2013, but as of 2014, version 1. 0 continues to be more widely used.
HarmonyOS is a multi-kernel system. It uses the Linux kernel and a modified LiteOS kernel. Unless they mean to eventually move past that, but idk, this article is trash and doesn't say much, it just sucks Huawei's dick.
Nobody should care about some dodgy proprietary OS with CCP backing.