it's almost never a simple function of population. One example: between 2010 and 2020 population of Latvia dropped by about 10% while the house prices have doubled.
If it used to be that two or three generations of a family lived in a house and now everyone wants their own, housing demand could increase while population drops. If marriage rates or number of children per household decrease, housing demand per capita probably increases.
Right, population has been steady or even slightly declining, and there has been plenty of housing development, so it’s not a surprise that existing housing prices haven’t gone up. But even that directly contradicts the OP’s first sentence.