I understand where you are coming from with "fear not", but is that the same as promising the present Earth will persist in sustaining human life no matter what? The long anticipated "Tribulation" does not promise a world without end or a continuance of resources. I think the opposite is the expectation--isn't it?
I have not heard of any actual policies to kill off 80% of the population. That sounds horrible. The only thing I have seen in regard to population reduction is related to family planning and increasing the availability of contraceptives. In general, when countries industrialize--like the USA has, population decreases. That is just fact and is a function of how many children are desired by industrial and post industrial workers, which turns out to be as few as possible. Agrarian societies, on the other hand, have always had a sweet spot somewhere between 'enough children to efficiently work the land' and 'yikes, we have too many kids to keep fed!'. Meanwhile, the post industrial parents must balance the number of children with the cost of raising those children. No matter how they slice it, each additional child beyond zero offers diminishing returns and fewer resources to spread between the kids.
These are hard times. I do not know what evil plans evil people are up to, but whatever they are doing, I believe they are taking advantage of our hard times. "Chaos is a ladder" to quote a fictional evil character of popular culture fame. Russia, for example, is unable to feed their population without importing nearly half of their food. Why? After the fall of the USSR, they couldn't keep their farmers farming. Sadly they were unable to make a go of it and packed up and moved to cities. India and the Mid East are two regions that were traditionally a source of food for places like Russia, but catastrophic drought and industrialization has reduced the amount of food available for export. Does invading Ukraine seem to make more sense in this context?
China is similar. The rapid growth of their industrialized population want food and they can finally afford it. After catastrophic flooding on their own farmland, and the devastating loss of livestock due to the COVID19 outbreak, China has been importing food like mad over the last few years. Did you know that in 2020 when American and Canadian meat packers were forced back to work despite the danger of catching COVID19, they were packing meat not for us, but for the Chinese market? People died so that corporations could sell extra meat to China.
So, ultimately, there is a food crunch all over the world. The answer isn't killing off the population, however. Instead it is increasing food security. The population will naturally decline on it's own as we technologically progress.
I will add one more thing. Farmers being forced off their land, dumping of commodities (especially food), widespread homelessness, severe labour shortage yet lack of jobs that pay a living wage, hyper-inflation, and various other ills we are experiencing are hallmarks of market failure. We are suffering from bad economic policies.