I think that if you get into many of the BIG problems that sound really exciting, you'll find that they can't actually be solved. My first startup idea after striking out on my own was to fix unemployment, which was a big, impactful problem that disproportionately affects underprivileged people. As I researched the problem, though, I realized that it's not really something that can be fixed. Hiring is hard because it's fractally fucked up: it's a many-participant market where everybody rationally follows their incentives but the sum total of those incentives is a system that massively underutilizes human potential and makes everyone miserable. Now, you can fix individual problems within the space like finding job postings (Indeed), tracking applicants (Lever), giving coding tests (TripleByte), etc, but each of those just makes life better for the person giving you money, and arguably makes the system as a whole even more fucked up.
The same goes for many other hard problems. Political polarization in the U.S. is a huge problem, but there's no one solution that will fix it short of mind-controlling or eliminating everyone who disagrees with you. Alleviating poverty in the developing world is a huge problem, but countries that are poor today are usually poor for a constellation of different reasons, and unless you fix them all you're not going to make the country un-poor.
The author seems like he's deliberately avoiding any areas that are not product-fixable. That limits his list to fairly boring problems. It's likely hard-won experience as an entrepreneur, though: I know that I started the entrepreneurship journey thinking I was gonna solve everything and have a big positive impact on the world, and have since learned that unless you adjust your expectations, you are bound to be perpetually frustrated.