I wish for all systems of capitalism to collapse to be replaced by something better for the most people possible.

Granted. Humans go instantly extinct, all their needs and wants become moot.

But what’s the downside?
- Well they'll be a bunch of abandoned pets at the very least. Some nuclear reactors probably won't do well being in the middle of service without supervision.

Granted. World War 3 breaks out which brings the worst human's rights violations that you can think of, followed by nuclear annihilation.

Sure, capitalism fell but so did 95% of humanity. What remains are some small groups of people suffering in the post apocalyptic hell, and the ultra rich who enjoy a life of luxury in their underwater bunker city.

How is that different from the impending climate crisis?
Since my wish clause is that things have to get better for the most people possible, if the poor people in small groups suffering manage to become 51% of the living humans then something would go wrong in the underwater city like it springs a massive leak killing all the ultra rich.

The massive leak of good nutrients gives some new food source to a species just managing to survive. This species with a food source thrives giving the opportunity for the small groups to coexist on the razor edge of survival as long as they live in harmony with the species.

Granted . The plot to the Matrix movie series is a reality: general ai is made, the ai moves to inhospitable land (Sahara Africa and Antarctica) ai produces more high quality goods for lower cost than 3x the rest of the globe combined. The rest of the globe goes to war, and wars are won on logistics(aka the ai won). The ai decides to create a immersive "matrix" to simulate whatever humans want and keeps humans locked in what they want the most. Some want to live in the 90s. Some want to ride in a ship called Nicodemus (because they remember hits that this world could be a bad dream) some have delusions of waking up (but in reality, they did not).

The ai removes all capitalism from its simulated matrix and any recursions of "matrix within the matrix" that get created from time to time for troubleshooting.

Long term aftermath: the ai communes with god and makes changes to its matrix to maximize what god wants, so the matrix now seems most similar to permanently pre ai with lots of decisions. the ai cleans the environment on earth and explores space.

This sounds ideal, since the world is better off this way and my wish for the most people to be better of just requires 51% of all remaining humans be doing better.

In fact if the matrix wants to keep 10 people around and only have 6 of them be happy my wish is still fulfilled.
- All hail the Algocracy. Actually kinda interesting considering the recent memorial of Pinochet's actions and how he helped snuff out a nascent example of an algocracy.

Granted. Because all capitalist systems have crashed, nearly all the world's wealth and resources are now in the hands of a tiny number of people. The new paradigm allows only those few people to live in luxury. The most people possible is now around 350.

Something better? You have to find something better that won't end in a absolute Desaster.