In my fictional world, Moon City is real, already finished and successful. It's made by fictional and made up people

Yeah, that distant future isn't so distant anymore. In fact, it's actually pretty close to us!

There are already ancient ruins of cities on the moon that's what NASA has been studying up there 😄

Can't, its already inhabited on the dark side… thats why we never went back.

We will have city if Elon musk want a city

US and China alone combined have a military budget of more than $1 trillion, spending at least half of it on space programs, we could build a small city on the Moon and even on Mars…

Make a video of terrafroming mars or titan

16% Earth G is difficult to depict in video, and to wrap your mind around.
We can't know if we can stay healthy in low G if we lived there long-term. The Heart and every other tissue in us likes being moderately stressed, often or all the time.
We have zero data on living on low G, and it's not safe or responsible to talk about living and raising children there until we know. We do know that animals raised in hypergravity in centrifuges are stronger, and more healthy and live longer than controls, and we know that someone who exercises a lot will be expected to live longer than a couch potato.

Fortunately we can live in space colonies in virtually Earth-like conditions, and the domed Lunar city would be there, for those that don't mind taking the radiation doses that would get through any transparency we can think of building a dome of. Armor glass would do, but it'd have to be over a meter thick to stop galactic cosmic rays and the secondary particles they knock off from any insufficiently thick materials you put in front of them. There was a proposal to us layers of water 5 meters thick, and if it's pressurized to Earth Sea level, air pressure helps hold it up (you could literally fly with a pair of wings strapped to your arms).
Note that if someone jumped into a pool or lake, the hole would be big, take a long time to fill in and the surface of the lake would slosh about with tsunami coming up on every beach for hours if there weren't strong wave dampers.

He3 is irrelevant, even if someone figures out a good way to use it in fusion reactors.
Long before we'd get useful amounts of it back to Earth, Solar power satellites from NEO materials would be powering the Earth. (We know of 400 NEAs (among the ones most likely to hit us someday) that are easier to reach than the Moon. 40 or so easier than Lunar orbit. They'd also have much better resources than the Moon.
The Moon is called the slagpile of the Solar system because its best resources are about what an asteroid miner would toss aside as not economical to process further. It also dos not have lots of water. If there were concrete in one of those permanently shadowed Lunar Polar craters, they mine it for its vastly superior water content.

Long before we are building a city in space or on the moon or more than a sparse base at/on Mars, someone will bring back samples of previously rare and precious & "strategic" metals from an NEA, and the funding question goes away along with the national debt or any budget austerity demands. Also the need to fight wars over access to oil and minerals down here ends. Note please that we spend far more on warfare than on space. Today the US annual DoD budget is ~80% of the entire historic running grand total NASA expense. Counting Apollo, the Shuttle, and the ISS, but not counting "black" military budgets and ongoing operational military expenses, each of which is more. During the entire timescale of Apollo, the US spent as much on cosmetics, and large States spent more on liquor than we spent going to the Moon.
Far less than a small oil war would pay for the NEA mine and small early first generation space habitat like the Stanford Torus or O'Neill "Island One" Bernal sphere habitat. We'd be learning to protect the earth from the most likely impactors, and we'd get the Moon, bases on Mars, and an end to oil wars and resources scarcity and be proving the means to end heavy primary, polluting industry down here.
The findings of the NASA Ames space settlement studies of the '70s are available to read online, and say that no new inventions are needed to start. All the potential new processing and manufacturing methods we might use up there are known down here; some in use, others as minor effects or difficult in gravity.

When we Build Cities on The Moon, we're going to enter a new Era of Human Civilisation where we're free from Religion, Superstition and the Conservative Mindset we have on Earth.

Science and Technology will flourish and guide Human Civilisation to the Next Big Step of becoming a Galactic Civilisation.

Above all well see Earth Rise, and It's so cool 🤗❤

So… if I'm a moonling, will they call me a Lunatic?