What if the common trend of 'house prices rising totally out of whack' amongst various locales (Canada, USA, Europe, Australia, China) is not.. actually, a common trend? No single explanation suffices; it's just coincidence.
Low interest rates raise house prices. This has to be a 'duh' thing, really, but, governments don't really appear to 'get it', or, play dumb for political reasons. If, after adjusting for inflation and the like, the exact same house costs €500,000 in 1980 but costs €1,000,000 in 2024, BUT, interest rates in 1980 are double what they are in 2024, your mortgage cost to buy that house is __pretty much identical__.
It's oversimplified to say that this means 'real house price has not changed'. It still takes more money to actually buy that house. But, of the money you pay every month for your house, more of it is a weird, not very liquid investment portfolio, and less of it a weird form of rent. It's got all sorts of problems: Not everybody qualifies for a mortgage in the first place, for starters. But _in the end the amount of money you have to burn just to live in a house is identical in this hypothetical scenario_.
One lesson you could learn from it is that everybody is whining and houses are just as affordable as they've always been, but that's not my point, and isn't really true. The point is more: With low interest rates, house prices skyrocket.
This explains _some_ high house prices, but certainly not all.
For example, China's is an utterly different explanation. Due to the way their government is set up, the usual benefits of a free market, namely that the population 'intelligence of the masses' their way to efficient allocation of resources isn't a thing china 'does', in essence. Government decides what happens. And so far, they've decided to build more houses than there will ever be chinese people to live in them. Ever. This is a bit of a problem today and will be far more of a problem tomorrow. But that's it. That's the simple, sufficient, and therefore only required explanation. It has NOTHING to do with how hard to it is to build in China (it is not), nor with population growth (it doesn't, or rather, a sheer and severe drop in house prices looming, that'll be explained by China's population glut). It's just that: They built way too many, and their market system cannot respond in kind to stop that runaway process.
In europe, yes, in large part runaway NIMBYism and being at the forefront of ecological change, putting limits on how much nitrogen/co2 can be 'used up', and building does take quite a bit of that - has put the breaks on building. Especially combined with extremely low unemployment which hurts the building sector. "Too few houses being built" is a factor.
But not the only one. And I think, not even the largest one.
Yet another explanation is lack of efficiency: Fewer people partner up, so, more people live alone. They tend to use space inefficiently: They all want their own kitchen, their own shower, their own living room, their own bed room, their own hallway, and so on. A really cheap and ludicrously efficient solution to _that_ is dorm-style living together. Instead of having a small crappy single-tenant kitchen, why not have a giant luxurious very well stocked kitchen you share with 9 other solo tenants? Yes, there are all sorts of downsides to this (which lout has made a mess of the kitchen?!? - and nobody wants to deal with a cleaning schedule), but in the end it is vastly more efficient, and better for social cohesion.
Society in e.g. europe and the US has not, yet, adapted to it. I hope it will. It'll solve the unaffordability of housing crisis all on its own if society wants to invest in it.