Of course they have the capacity to build nuclear weapons. They did long ago. They are sitting on a huge stockpile of highly enriched uranium. If they have not actually built nuclear weapons, it is for political and strategic reasons, not technical.
Also, the Chinese Communist Party is doing everything it can think of to incentivize the six major Chinese EV companies to take market share away from Tesla.
It helps that Elon stupidly gave all his tech secrets to China.
That assumes that the Russians would stop the killing if they were allowed to completely conquer Ukraine. Everything that they’ve done shows that that’s not the case - just look at what they did to the civilians they massacred in Bucha. They commit mass rapes and tortures and summary executions in the areas they conquer.