The geniuses can still make very valuable contributions to humanity. It's just that the general public will have a hard time understanding a new achievement. We already see this everywhere. "Higgs Teilchen" and so on. The media showed it, nobody cared and everyone was confused (found at the CERN in geneva). It only makes sense.
We still make immense progress, but in very detaily branches often, that people just want to use but not having to know about, because of the sheer complexity.
I wonder where the borders of humans will be. :) We might not be far from them anymore. Nowadays, to get into unknows territory, you need to do scientific research for decades often and an exceptional brain. Because you need to get the basics first, to which others created the paths.
The next real innovation I see will be affordable space travelling and populating other planets. Other than that, some minor stuff will be implemented like nuclear fusion reactors and the like.
The hardest thing will be to define "individuals" who contributed some of that stuff alone, as it used to be in the past (more or less).
That's what the idea is. Once someone has figured out the basics eg energy conservation, relativity, etc, what's the next guy going to do? Put a small wrinkle on it at best. So the detaily thing is actually not immense progress, it's some small modification or application to a niche area.
The closest equivalent I can think of these days is Satoshi Nakamoto - assuming it's one person. But even their discovery is in a subfield of a subfield.
But there don't seem to be as many, or as much of a percentage of, people wanting to do hard work either.
You've landed a great list of worthy causes though, respect.
...but I'm not convinced any of them are low-hanging fruit. Almost everything on this list would require sustained R&D across several fields of expertise, and many of them have the significant added challenge of overcoming entrenched interests / power structures.
That's not to say we shouldn't try! Solving even a small part of anything here would materially improve quality of life for a lot of people - but these are not "I could solve this in a weekend" problems; these are generational problems, towards which meaningful effort could easily be measured in thousands of person-years from entire teams / organisations / ecosystems of smart people, and where even a chance at success would require a steady supply of adequate resources that is durable across periodic economic shocks.
CERN is the closest thing I can think of as a useful mental model here: sustained cooperation across multiple nations, massive amounts of public investment, clear tangible outcomes over a period of decades.
Perhaps it requires genius?
Same thoughts. Even though we, as civilization, had less resources in the past to discover "the world", one person could "easily" study the whole body of knowledge accumulated over the years and try to come up with something new. Add to that that the person is a genius, and you get something remarkable. Nowadays it's, imho, impossible for a single person to learn the whole body of knowledge of any single branch of science or arts.
Right now discovering a new phenomenon or topic in math or physics is virtually impossible.
Influencers with no factual knowledge but a strong opinion gather eyeballs and sell ads much better than a scientist with a nuanced opinion and a difficult niche topic to talk about.
It also doesn't help that the general public in the west is somewhat hostile towards the idea that other people might be a lot more intelligent than they themselves. It's like the temporarily embarrassed billionaires, but for IQ.
And it's not what you know that matters for fame, it's how good you are at selling yourself. Well, either that, or you get very lucky and the media picks up your story.
You can see a possible example of a genius getting media coverage in a niche area by looking at Kaze Emanuar and his Super Mario 64 mods. He's basically the best programmer for the system in the world right now, and has almost singlehandedly moved the community forward on every technical level possible.
His works also get a ton of coverage.
Yet I had never heard about him before. And while I could find a hackaday article, I didn't find anything more mainstream. So I would estimate that 99.9% of the population will never hear about him.
Could the 'mainstream' media cover every genius or great creator? Probably not, there wouldn't be enough room. There are so many great people creating works and making discoveries that you likely won't ever know about more than 1% of them, at most.
It's hard for me not to think that the kind of people who write what you just wrote think of themselves as the superior ones. And that's an instant turn-off.
Or you have a specific example in mind that I could use?
Probably the last, since no one has topped him yet... and physics departments have shrunk over time.
OTOH, to your specific point, research has become more directed; funding is in specific areas. Einstein himself had his initial insights outside a university context. Feynmann's diagrams developed when he decided to just "play" - i.e. outside his proper research.
I like to think there is gold just a step or two off the beaten path - but have no evidence for this.
Society back then was different and part of that was, that the gathering of knowledge, a nerdiness and enthusiasm for the new, was seen as something distinguished. Gentleman after the renessaince, bragged with book cases, private studies, curiosity cabinets and private museums.
Add to that the lack of enterntainments and distractions, against which a chemical experiment set or a rocket kit had to not compete against, and you are getting closer to the answer. Back then, you might read a lexica for entertainment, and think the whole day about it, while doing something else.
However, I have always thought that the answer to the question "What happened to all the geniuses?" was somewhat obvious -- we ran out of an abundance of low hanging fruit to discover. The 'ease of discovery' for breakthroughs in science and math are on a some sort of a non-linear curve, and they aren't getting easier.