Is it permissible to invest a sum of money designated for purchasing a house in an interest-bearing savings fund, given that it is currently insufficient for the purchase, and if that is forbidden, how can its value be preserved from inflation without the ability to trade?

It is not permissible to deposit money in interest-based (usurious) banks or savings accounts with a fixed interest rate, because this constitutes usury (riba). If the deposit is for safeguarding the money, it is not permissible in interest-based banks except in cases of extreme necessity (such as fear of theft), and in such a case, it should be placed in a current account that yields no interest. It is advisable to keep money in branches of Islamic banks that do not specify a fixed profit percentage but are subject to profit or loss. Allah safeguards the religion and worldly affairs of those who fear Him.