Hmmm strange. A 5700 XT is new enough to support NWS. Maybe something with the drivers or the DirectX11 version.
On the population density, I will probably go with some country-wide scaling factors for a number of years. Later maybe see how individual population centers behave or find complete population density maps for the cold war years.
Here you can find the current population density map:
https://ec.europa.eu/jrc/en/publication/ghsl-data-package-2019
I think they have maps dating back to 1975.
I had to write a script to convert the data from their format to the NWS format. It would be a total nightmare, to do it by hand :D (maybe it should be adopted as a form of punishment for criminals...)