I believe the properties are officially owned by his son-in-law, who is all juiced up from Saudi money and well within the billoinaire wealth range. But being a part of the Kushner family, with access to a near limitless pool of cash/credit, makes you at least as much of a billionaire as anyone on the Forbes List for all practical purposes.
Trump's biggest problem isn't cash flow, its that nobody (reputable) wants to do business with him anymore because he reflexively stiffs them all.
he’s probably got negative 90k sqft in Manhatten
I remember Hillary Clinton bemoaning her $25M in campaign finance debt following the 2016 election cycle. Credit lines that large don't get handed out to just anybody. They're what let you do crazy ass shit like buying Twitter at its current market cap because you went on a posting bender over the weekend.