How do we respond to those who deem interest (riba) permissible in this era due to inflation, arguing that returning the same amount after a period represents a loss for the lender due to the decrease in purchasing power?

None of the scholars have ever said that usury is permissible, as it is one of the destructive sins. As for inflation, the majority of scholars believe that the repayment of debts should be in kind, not in value, and that debts are to be settled with their equivalents. Therefore, it is not permissible to link debts to price levels. The lender is not a loser, for he is rewarded by Allah, and the change in currency value might even be in his favor.