Germany lost as many young men in WWI as the French did. Yet Adolph didn’t seem to lack for troops to invade France.
And had he not pivoted to invade the USSR, there’s no reason to believe he couldn’t have conquered western Europe, England excepted. Demographics wasn’t France’s problem.
That was the French explanation, and I agree with their assessment; families had shrunk, while Germany was still producing another generation of soldiers.
The invasion of the USSR wasn’t by Germany alone (Eastern European countries along the border, dealing with their own communists supported by Stalin, joined the effort), and after the Russian surrender of 1917 it wasn’t an illogical move. Without massive aid from the US (and Japan’s insistence on fighting China instead of the USSR), the Axis was beating them.
Hitler gave medals to German women every time they had a baby.
Hitler did conquer France, Belgium, Denmark, Norway,and the Netherlands. Spain was ruled by a dictator friendly to Germany and Italy. Portugal was neutral, as were Ireland, Switzerland, and Sweden. The only Western European nation that was hostile was Britain. But the Luftwaffe was defeated in the Battle of Britain, and the German navy could not have withstood British naval might. Therefore, an invasion of Britain was never undertaken.