We have a lot more infrastructure than Europe had at the time of the Black Death. If we lost 75% of the population, it might devastate things like the power grid, water supply and purification, etc.

We have (I think) more complicatedly interdependent institutions than Europe at the time of the Black Death. Relatively small upheavals in, e.g., our financial systems can cause a lot of chaos, as shown by our occasional financial crises. If 75% of the population died, how robust would those systems be?

The following feels like at least a semi-plausible story. Some natural or unnatural disaster wipes out 75% of the population. This leads to widescale failure of infrastructure, finance, and companies. In particular, we lose a lot of chip factories and oil wells. And then we no longer have the equipment we need to make new ones that work as well as the old ones did, and we run out of sufficiently-accessible oil and cannot make fast enough technological progress to replace it with solar or nuclear energy on a large scale, nor to find other ways of making plastics. And then we can no longer make the energy or the hardware to keep our civilization running, and handling that the best we can takes up all our (human and other) resources, and even if in principle there are scientific or technological breakthroughs that would solve that problem we no longer have the bandwidth to make them.

The human race would survive, of course. But the modern highly technology-dependent world would be pretty much screwed.

(I am not claiming that the loss of 75% of the population would definitely do that. But it seems like it sure might.)