@Rusty this might be the first step of what I was saying.
No doubt iOS and Android are very popular and it would be hard for a third OS to compete. However it was a bad move on the part of US to "politicize" android as an "American" system that can be cut off at any time. That's bad for business...all of a sudden it was a wake up call for companies around the world that they either play ball or can be cut off at a moment's notice. This creates a need for an alternative OS that is either completely open source(not in control of any country) or in control of the country that wants out from US controlled OS(like China for example).
Next is the challenge of
creating demand AND a
broad developer base with a large app selection and services...both simultaneously. This can be easily achieved if these companies band together and create an off shoot of AOSP(android open source project)...or work with an already existing off shoot like LineageOS...
With that they can solve the problem of developers having to create or port their apps on to this third OS...as for wide adoption...they already have a large domestic market. This in addition to throwing some large sums of money at it for a good 5 years should give it the initial push to emerge as a stable alternative that all Chinese phone manufacturers can adopt for their Chinese market(or possibly even other markets like India, Vietnam, Phillipines, etc.)