I think what's more likely is a fertility decline that causes greater instances of infertility in people who want kids (among my friends and family, there is increasing levels of infertility, including in myself, and I'm only 29, there's also a lot of news about sperm count decreases in Western men due to either microplastics, chemicals or some other factor), plus social changes that increasingly lead to women deferring motherhood (and thus reducing the number of kids they have). As such the population is likely to decline considerably in the next hundred or so years even without some apocalyptic level event that kills billions of living people who aren't dying of old age.