Tax homes based on how many you own, and how many are vacant. Allow two homes at a regular rate; Enough for a summer and winter home. Then ratchet tax rates up as the person buys more.

And if the third, fourth, fifth, etc home sits vacant for more than a few months out of the year? The tax rate goes up even more, so giant corporations can’t just buy entire neighborhoods and sit on them to remove them from the market and increase property values for the other homes they own across town. Because that’s what’s happening now; Giant corps are buying homes and letting them sit vacant, just to remove them from the market so they can charge higher rates elsewhere. Allow a few months of grace for renovations and finding tenants… But after a ~3 month grace period, that tax rate skyrockets.

Incentivize the corporations to actually flip the houses and resell or rent them, instead of just sitting on them.