Unlike the vast majority of other human endeavors, land actually is a zero sum game, at least until we are a space-faring species.
* Within the Solar System the amount of land available on bodies with not-crushing-gravity is limited to a few times the Earth surface. This includes hospitable bodies like Venus, Titan or the Moon. The entire area of Mars is slightly smaller than Earth's land area, with climate conditions significantly worse than Antarctica. Sobering map: https://brilliantmaps.com/solar-system-surface
* Inter-stellar travel is subject to prohibitive time and energy costs. Physically speaking there is no way for Alpha Centaurians to visit their Earth properties on a regular basis, or vice-versa. This renders the whole concept of 'property owned by foreign stellar body inhabitants' moot.
Around 17% of the Netherlands is reclaimed from the sea or lakes. The largest project (the Flevopolder [1]) was 240,000 acres, reclaimed in the 1950s and 1960s. Most of the land is still just meadows/grasslands (it has 2 towns with less than 350k inhabitants in total).
Meanwhile, in Amsterdam (less than 30min away by car or train) house prices keep increasing by 10%+ YoY. It seems that lack of physical land is not the main limiting factor.