How can a Muslim secure income in old age, given the depreciation of money, and avoid relying on others, especially if working in Western countries, since an optional retirement system is not permissible?

Social security or insurance is permissible under conditions: the owner's consent, that it is cooperative and not commercial, and that its funds are not invested in what is unlawful. If these conditions are met, participation is permissible; otherwise, it is not. If the conditions are not met, there are lawful ways to grow wealth, such as depositing in an investment account with Islamic banks. "And whoever fears Allah - He will make for him a way out And will provide for him from where he does not expect." The Prophet, peace and blessings be upon him, said: "Indeed, the Holy Spirit inspired in my heart that no soul will die until it has completed its provision and its term, so fear Allah and be good in seeking."