Chinese Civil Aviation and Shipbuilding

From an interview with Aeroflot general director.

The C919 is the same aircraft as the Superjet or MS-21 in their non-import-substituted versions. “That is, the chance of this Chinese aircraft getting into the fleets of Russian carriers is zero, even if the Chinese themselves want it.”

Same aircraft here means that it has a very large share of Western components and can be easily grounded due to sanctions.

So China cannot sell it to Russia, but also not to Siria, Iran, Venezuela and Nord Korea.
What China did here is not more than what Brasil did with the Embraer E-Jet series, except the size of the aircraft is bigger. That is, they produced the fuselage and some other parts and imported everything else. (And in most cases, the suppliers are the same that supply Boeing and Airbus aircrafts).

Maybe Russia could propose China to help them certify an alternative version of the C919 without western components (e.g. with PD-14 engines and with the avionics, navigation and other internal system developed for the Russianised MC-21).

The problem here would be the engine, as the current foreseen engine production rates, even taking into account the second assembly line, are barely enough for the planned MC21 production.

Anyway, even if Russia solved the issues limiing the engine production rates and became the main suppliet for a western content free C919, it would not make sense for Russia to buy them, as they would just be a worse alternative to the MC-21.