Last time I checked Android IS BASED ON LINUX and only one layer of Android 9 is open source. Hata wewe ukitaka ku-download and modify just go to source.android.com. The main problem of that version of Android is that it lacks some layers which are critical. And for you to access the proprietary version of Android you must be in good terms with Google. Huawei is free to use this version and deliver a similar UI experience. Problem is that no-one will trust Huawei especially when it comes to security updates and creation of backdoors. The same thing that Google did in the early years of Android.
The easiest option for Huawei is to restore it’s relationship with Google through political means. In the long run though, the solution is to develop a better open source OS which eliminates the shortcomings of Android.
The truth is Huawei cannot challenge google in phone OS. Bigger companies such as Amazon, Microsoft and even Samsung tried but failed terribly. It’s almost impossible to replace Android today not because it’s American but because it has created footprints in our tech ecosystem that cannot be replaced. Building an OS is not a big deal any company with enough resources can do it, but having consumers use it could remain a pipe dream. That is the same reason why even the mighty google was unable to replace Windows to date. Google is not just about the Android OS but the services it offers which most of us can’t replace. Imagine Youtube, Gmail, Google Maps and the rest that will not be on Huawei phones.