Is buying a house in installments over four years with bank interest permissible or forbidden, given the inability to pay the amount in cash and the desire to keep the current apartment?

Purchasing an apartment through usurious banks is forbidden, because it is a loan with interest, which is usury (riba), prohibited by the Qur’an, the Sunnah, and scholarly consensus. The one who engages in it must repent to Allah. As for the loan itself, it appears to be valid. Therefore, the questioner is only required to repent and return the principal amount, and the house remains his property.