We're talking high-rise apartments here.
https://www.answers.com/geography/Can_the_population_of_the_world_fit_into_the_state_of_Texas
Not sprawling suburban McMansions, no, but, still livable, if you could figure out infrastructure. Which honestly sounds a lot like the BS 15 minute cities that are being pushed now.
Discussion
No, we aren't. Though, they are certainly not efficient, space wise, and we're also not really treating families as anything more than just individuals, too.
My home is only about 240sqft. Could live on a thousand square foot lot of I had to, but I don't want to.
Sure, cities are fine for some people, and anyone that wants to can live in one, but I don't think that's good for humanity, long term.
The math doesn't work.
We are: 8,000,000,000 people
Earth has: 148,940,000,000 meters ^2
How many meters should each person get?
Kilometers squared, my dude. Not m^2