Sino-Russian conflicts are old going back to the colonial days andInteresting. I was under the notion that Russia - China border issues have been fully resolved a while ago.
Even if there is proper credence to the above cited aspersions, I don't think Russia is a position to do anything that will antagonize China. For the Russian people to continue with their present standard of living, the Chinese energy market is very important. In some ways, the Russian economic dependence on China is not very different from the Canadian dependence on US. Russia is trying to mitigate some of the dependency by selling gas to Europe, but Germany will eventually go green.
As things stand today, we see that Russia has sold some of it's most coveted military to tech. China. This cannot have happened if Russia was not comfortable with China. Eventually, the American politicians will have to find a way to wean Russia out of China's sphere of influence. This is not going to happen anytime soon.
Sino-Russian border conflicts
no border resolutions will solve the enmity between them unless Russians willing to part with entire Siberia to Chinese
You are correct Russia being no longer a superpower does not confront China overtly
They do so in subtle ways such as assisting India with nuclear submarine development etc