What is the legitimate Islamic solution for a contract to purchase an apartment in installments, whose terms stipulate that the ownership of the apartment will not officially transfer to the buyer until all its installments have been paid, while allowing residence in it from the date of signing the contract, and with no money or assets available to be mortgaged to the seller?

The condition that ownership of the apartment not be transferred in official documents, and that the buyer be prevented from selling it until all installments are paid, is permissible. This falls under what is known as official mortgage (al-rahn al-rasmi). The condition to terminate the contract if the buyer delays payment is permissible. However, the condition to pay financial compensation upon termination is not permissible.