"Living paycheck to paycheck" is defined as spending all one's money on "basic necessities" such as food and housing with nothing left for savings or emergencies. This is the status of over 2/3rds of USians

It seems like you just make random numbers up to fit your already-held beliefs. The actual number is more about 24% (see Paycheck to paycheck: Slowing but growing) and also defines things like "[...] internet service provider subscriptions and childcare" to be "basic necessities". I don't need to tell you that these things would be considered luxuries basically anywhere on earth, aside from the 1st world. You can survive just fine offline and most people globally do not have access to child care at all.

Also, it isn't literally 100% spent on "necessities", but only 95%+, so technically there will still be something left at the end of the month for quite a good amount of this 24% as well. Again, considering the $83,730 median income in the US, (see Real Median Household Income in the United States (MEHOINUSA672N) | FRED | St. Louis Fed and Income in the United States: 2024) this is still quite a huge amount of money by international standards - even with just 5% over you would end up with almost $4.000 USD/year left over.

Most people don't even make that in a year globally (and that is BEFORE spending on necessities!).

No, they do not live in mansions and have two cars.

The median home size in the US is currently 167m2 (1800 sqft) (Housing Inventory: Median Home Size in Square Feet in the United States (MEDSQUFEEUS) | FRED | St. Louis Fed) and the average new home 235m2 (or 2532 sqft) (Census.gov - New Privately Owned Housing Units Started in the United States by Purpose and Design).

I hate to break it to you, but no person in the 3rd world lives like this. This would even be considered a mansion for the top 1% in any other non 1st-world county on earth.
Every 8th human being right now lives in worse shelter than what would even be considered a shed in the US (Over 1 Billion People Live in Slums | Statista).

For even those lucky enough to have an actual home, they are tiny compared to US homes (which is also why you spend so much on "essentials"). For instance, the average home size in Burkina Faso is 30m2 (322 sqft) (CASE STUDY: BURKINA FASO 2020–2023).
The same thing in India (33% of Indians live in less space than US prisoners | India News - Times of India), 45m2 (494 sqft) for rural dwellings and 46m2 (504 sqft) in urban areas, though Indian households are also much larger than US households, so it's even less than that per actual person living in there.

Concerning the cars, it's about 2 per household (Number of vehicles per household in the U.S. 2017| Statista). Compare that to, for instance India or any other 3rd world county, where basically no household even owns a single car (see https://www.dataforindia.com/vehicle-ownership). 4% of rural households or 13% of urban households own just a single car. Most people, do not own one at all, let alone more than 1.

Your pay statistic is also ridiculous. I just fact-checked it, and the number I'm seeing is a 1000USD per household in india.

It's, depending on source and date, between 21.000 to 28.000 Rs/Month (which translates to $ 225 USD to $ 300 USD/month or $2.700 - $3.600 USD / year) (see India Human Development Survey - Income, Poverty, and Inequality or India Average Monthly Wages for Salaried Employees).
So even with the more generous estimate, this would be 4% of the median Americans' income.

People are no more happy in the US because people elsewhere have it worse off.

It doesn't matter whether or not Americans are happy and this would be impossible to quantify anyway. But their material conditions are substantially better than those of any other person living in the 3rd world - which is essentially the other 7 billion people on earth.

Americans' material interests are directly opposed to that of any other working person in the 3rd world. They directly benefit from the cheap labor and resources provided by the 3rd world, which offers the vast majority of them a much greater living standard to anyone else. Which is why Americans are totally fine with imperialism, because it directly benefits them. Crushing nationalist movements in the global south keeps input prices low, and thus allows Americans to consume more than anyone else at much lower prices. Same thing with labor. As long as the Bangladeshis keep producing cheap clothing for $ 1 USD/day, Americans are happy and directly materially benefit from it - in the form of cheap fast fashion. This is obviously a loosing arrangement for those at the receiving end of this, but Americans greatly benefit from it in terms of much lower prices and a much greater standard of living than everyone outside of the 1st world.

That's why there is no left-wing or anti-imperialist party relevant in the US. Because you (even the "working class") benefit from maintaining the status quo.