The Star Trek future may be right on schedule.
https://memory-alpha.fandom.com/wiki/World_War_III
World War III was the last of Earth's three world wars, lasting from approximately 2026 to 2053. The conflict involved nuclear cataclysm as well as genocide and eco-terrorism. The post-atomic horror in the aftermath persisted as late as 2079.
The war was preceded by the Eugenics Wars and the Second Civil War, all of which were sometimes regarded as parts of a single escalating conflict. It resulted in the deaths of some 30% of the Human population, at least six hundred million people, and the extinction of six hundred thousand species of animals and plants. By the end, most of the major cities had been destroyed and there were few governments left.
> some 30% of the Human population, at least six hundred million people
The math nerd in me has to point out that this means there was only 2 billion humans for 30% to be 600 million (though it does say at least). Currently we have 8 billion humans on this planet or so. There must have been a culling before WWIII in their universe that they failed to mention.