A lot of people don't really understand what China means by "developing the productive forces", so here's an analogy. In 1800, the US was a bourgeois/capitalist republic, but its politics were dominated by the slave-owning aristocracy. Two modes of production existed at once.

The level of development in the US at that time meant that owning slaves was far more economically viable than wage-labor. The mercantilist North couldn't outcompete the semi-feudal aristocracy of the South, so they worked in tandem to economically develop the country.

Eventually, the development of new productive forces like the cotton gin and the steam engine greatly empowered the Northern capitalists at the expense of Slave Power, and wage-labor became more viable than slave-labor. This heightened the contradictions in the US.

The Civil War was a result of this changing power balance, as Slave Power was quickly losing its relevance. Since the US was a bourgeois dictatorship, the slave-owning aristocracy could not stop the developing forces that were destroying their power within the system.

By developing the productive forces, the US was able to break the back of the slave power that helped develop the US into a modern capitalist state. It was a class struggle between the bourgeoisie and the aristocracy, and capitalism was able to win out in the end.

China is in a similar position. It is a DotP that exists alongside some bourgeois social relations. Like slave power helped develop capitalism, capital is helping China develop socialism. New productive developments will slowly erode the power of the Chinese capitalists.

The quote "The capitalists will sell us the rope with which we will hang them" is relevant. The transition from capitalism to socialism to communism will have a mixture of new and old social relations, there is no hard line between modes of production. China is in transition.

The development of new technologies like 5G, AI, renewable energy, blockchain, and cybernetics will all erode the power base of the capitalists. "Socialism by 2050" means that China will have developed socialism by then, there is no "socialism switch" to be flipped in 2050 by Xi.

Dialectical Materialism posits that nature and society is an ongoing process of development. Change is a constant; it happens slowly then all at once. The class struggle will continue in China, and its DotP means the workers have the upper hand.