For some reason I am unable to copy and paste links on my phone. Google Russian demographic decline. Along with the the plethora of articles there is occasional, “hey, it’s there but the significance is overstated” article. But even those present terrible sounding data. Also, go to youtube and type Peter Zeihan and Russia. He’s a former intel analyst.
In all honesty the decline from 148,5 million in 1992 to 146,2 million in 2021 doesn’t look too dramatic.