> If we don't want the entire earth to looked like mumbai

If the whole world reaches Mumbai's density (75k/sq mile), we would host 15 trillion people. Now, no matter what projections you hear from anyone, you never hear a peak population of more than 50 billion, so you are off by a factor of 300.

Here's for example the latest UN prediction up to 2100. You'll notice a 95% estimate that we'll be below 13 billion.

[1] https://population.un.org/wpp/Graphs/Probabilistic/POP/TOT/9...