I was thinking about your comment regarding maintaining population in both of these countries. Looking up the fertility rate for each it surpised me that Russia's (while really bad) is better than China's (which is really REALLY bad).
2021 numbers (quickest source I got both countries)
For reference, for a country to just maintain their current population the fertility rate must be 2.1 (meaning, every mother/father pair needs to give birth to 2.1 children overall). The other way a country can maintain (or even increase) their population is through immigration. The USA and Canada use this method fairly successfully even with both having native fertility rates below 2.1 .