What is the ruling of Sharia on grants given to retirees in exchange for their previously paid monthly subscriptions to the social security fund? Is it permissible to take these grants and invest them in a charitable project if they are not lawful? And what are the Sharia-compliant ways to reclaim the subscription amount?

It is permissible to take any amount exceeding the sum paid for insurance and spend it on charitable causes, because it is money acquired through a haram (unlawful) contract, and thus neither party is entitled to it. Its ruling is similar to "the price of wine, the dowry of a prostitute, and the gift of a soothsayer." Whoever willingly entered into insurance must repent, feel remorse, and seek forgiveness.