What is the ruling on purchasing an apartment in installments from a real estate company when a bank is a third party, such that the full sale price is transferred to the bank, considering it the mortgagor of the project until all dues are paid, and does it affect the ruling if the bank is usurious or claims to operate under an Islamic system?

"A ruling on something is a branch of its conception." It is not permissible to deal with interest-based banks unless the bank has a dedicated branch for Islamic transactions that is independent and has a Sharia supervisory board. As for the contractual relationship with the real estate company regarding the purchase of a residential unit in installments, mortgaging it while allowing its use, and then paying the installments to the company through the bank, which collects them for itself, there does not appear to be any Sharia impediment in this. Installment sales, mortgaging the sold item for its price, and the mortgagor's utilization of the mortgaged item with the mortgagee's permission are permissible. The permissibility of the transaction is not affected if the relationship between the real estate company and the bank is interest-based, as long as the buyer's action is free from usury and other Sharia prohibitions.