What will happen to bitcoin if the world population increases? I've been trying to find an answer to this question but without success. I have a question on scaling, but not of the technical kind.

Assume that the entire world switches to using bitcoin as its only form of money. What will happen with the fixed number of 21 mil bitcoins in an ever increasing population on the globe?

Will they just distribute thinner and thinner to all the people? Will its value increase? Will people just get paid a salary of 0.0000000132 BTC (or similar) in the future?
The amount of bitcion in circulation does not increase or decrease based on human population.  So, yes, it will likely be distributed more sparsely among people if the world's population increases.

However, bitcoin is only divisible to 8 decimal places, and your example uses 10.  It's also difficult to say what role Bitcoin will play as far as global currencies go, so it is unwise to assume that an amount as small as 0.00000001 will be equivalent to a modern day yearly salary (or whether Bitcoin will be used for salaries at all).  Speculation like that is off topic in this forum, which is why you've received some close votes.