I really need some advice because I feel like I'm missing something, but here in Finland after some basic calculation I just don't see how a mortgage makes sense, especially for someone ineligible for ASP (local savings scheme for first home buyers, but it has many restrictions).

Home prices are not appreciating (which I otherwise consider a good thing for society), tax breaks for mortgages were abolished a few years ago, rates are at about 3%, down payment and collateral guarantees (when you don't have local collateral as an immigrant) make for a pretty hefty lump sum. Throwing the numbers into a calculator and pitting them against a 6% annual ETF over 20+ years seems to be too much in favor of the ETF, even with potentially higher rent down the line.