Tax property values.
We could talk about the merits of Georgeism but honestly let's set that aside - conventional property taxes are sufficient here. Most of Manhattan apparently has cough), they're a tiny fractional "decommodification" of property as asset, because the money collected from the owners is spent on the residents. Most of this money passes through directly into higher rents, and we shouldn't care about that, because it's spent on the residents (if the residents don't want good public services, literally hand them a check, direct redistribution). This punishes vacant properties appreciably, and pushes them back into the market.
The ecosystem of debt and bank collateral that has grown around near-zero property taxes has strongly encouraged high vacancy rates, because the banks directly demand that what rents be collected, are high enough to justify the collateral valuation, but don't actually demand that rents be collected.
Set property values to the rate of inflation (depending on your preferences, CPI or local COL or local selling prices or S&P), and you have fully "decommodified" housing without lining the landlords up against the wall and shooting them, an option that is increasingly popular.