The world itself will end when the sun goes nova. But it will effectively end when humanity guess extinct.
We pass the point of no return on climate change in less than seven years. After that, the collapse of human civilization and eventual human extinction will be inevitable. The link below includes references that back up the science on that point.
https://climateclock.world/
The US military projects that basic infrastructure - electric and water service - will be failing within twenty years. The food and medicine chains will break, making supplies problematic at best. The military's primary task at that point will be quelling revolutionary activity by the by-then-far-vaster numbers of poor and desperate people. Controlling the information available to the people and propagandizing them into hate and fear of other groups (based on race, age, and politics) will be a critical part of that task.
As civilization continues to collapse, many of the elite will withdraw and retire to their luxury underground bunkers where most of them will probably die out within five years; without servants of slaves, they won't be able to survive.
Some of the elite may set up armed compounds guarded by squadrons of elite thugs. They're likely to live longer than the underground elites, but they'll still end up dying out in the extinction of humanity. These people need slaves to survive. Without them, they'll die.
The general human condition will get worse in the next hundred years. More and more of the Earth will become uninhabitable over that time, from the equator towards the poles. Mass migrations will take place, with huge wars fought over habitable land and resources such as water and food. Billions will die.
As the medical supply chain fails, plague and new diseases will spread uncontrollably. The endless mounds of rotting human and animal dead will be a major driver of infection and death. The Earth will become a charnel house.
No one will record when the last human dies. It could happen in a couple of centuries, or in five or six hundred years. But it will happen.
