declare bankruptcy because it couldn't cover its assets being withdrawn, how does it still have assets to now pay the investors back?

And, having found this, wasn't this the stealing part?

At the trial last October, some of Bankman-Fried’s closest collaborators accused the former CEO of knowingly funneling money from FTX depositors to his trading firm, Alameda Research, over a period of several years. Documents show that Bankman-Fried then spent those funds on Bahamian real estate, startup investments and political donations. “The money belonged to customers and the customers did not give us permission to use them for other things,” FTX co-founder Gary Wang testified.