A genie offers for you to change the world in one of five different ways. Each possibility has one huge benefit for mankind, but also one consequence

A genie has decided to use their powers to help humanity. They have spent a ton of time and effort thinking of the best ways to help humanity, using magic to explore countless timelines and the impact each of their ideas would have if implemented. however, a genies magic operates according to strange limitations and rules, and no matter what they try, it always seems to have some major consequences. As a result, they figured that they better leave the final decision up to a human, and they have picked you. After scouring possible timelines, the genie has decided that the best possible options are:

1: the genie grants humanity an infinite number of magic cauldrons which can be used to conjure infinite food. However, the cauldrons can only make unhealthy foods (cake, ice cream, really greasy pizza, etc.). Starving is instantly solved, no human ever dies from not having access to food again. However, general health of the population suffers. Healthy food becomes even more expensive, because hand gathered food is now a luxury, not a necessity. Many who were healthy before become less healthy, and diabetes rates soar in countries without the means to address it. Eventually humanity will address and mitigate these problems, but the genie tells you they will eventually do the same with starvation as well, if left alone and given proper time.

2: the genie makes cancer much more common and virulent. Now nearly every person will get some kind of cancer at some point in their life. This galvanizes humanity to fund cancer research, and a universal cure for cancer is found much much sooner. 150 years from now, there are fewer total deaths from cancer than in the scenario without interference, and 1000 years from now, over a billion more cancer deaths have been avoided compared to the no interference scenario.

3: Everyone with malaria, tuberculosis, and HIV instantly disintegrate to dust. All samples of these diseases are similarly destroyed. No one will ever catch or die from these diseases again, but the thought of the mass murder needed to achieve this is very disturbing to the genie. Plus, future research into these diseases leads to breakthroughs in science and medicine that now will never happen, or will happen on a delayed timeline.

4: the genie gives humanity access to technology that enables them to travel across the universe. They will not develop this technology otherwise, meaning humanity eventually dies when the sun expands into a red giant. With this technology, humanity persists untold billions of years into the future. However, many other intelligent races are exterminated by humans who come to their planets and wage war. Humanity eventually evolves and grows into an almost universally benevolent race of do-gooders, but not before wiping out countless other races.

5: the genie grants humanity technology that can be used to completely and freely alter the genome of human fetuses. Humanity uses this on every pregnant woman to rid the world of all hereditary diseases. However, further customization is made available to the rich/upper class only. They use this to create smarter, faster, stronger, and more beautiful children. Over generations, this eventually makes them into a distinct species that can no longer breed with regular humans. They view themselves as superior in every sense of the word, and regular humans are barely more than animals. Eventually laws are passed which favor the new race and discriminate against regular humans, who become heavily persecuted and essentially second class citizens. Persecution becomes so severe that hundreds of years from now, regular humans are driven to the edge of extinction, although protective measures are put in place at the last minute to preserve the species and prevent this. Relations between the two races are eventually repaired, but the regular human population never rises above a tiny fraction of the new race, and are still haunted by the disadvantages of generations of systemic persecution for millennia to come.

OR:

Option 6, tell the genie to do nothing. The costs associated with interference is too high, let humanity decide its own destiny and solve its own problems, for better or for worse. Some things are better solved without magic.