What happens if world population keeps growing and growing after 2140 tho?
Starting sometime around the late 1970s, the Mexican Peso started experiencing extreme inflation. By the late '80s, the price of a loaf of bread was thousands of pesos. The Mexican government introduced the "new peso" whose value was equal to exactly 1000 "old" pesos. In other words, they simply created a 1000-peso coin, but they called it a "new peso" instead of a "1000-peso" coin.
Bitcoin might one day have the same problem, except in reverse (because Bitcoin is
deflationary), but the solution is similar. Introduce a unit that's smaller than a single satoshi (maybe you could call it a dannyhamilton?). It would require a bunch of software changes, but it's entire feasible, and it's entirely fair.