Is it permissible to participate in a governmental company for brokerage in the stock market, knowing that it trades with individuals' contributions for a commission from the profit and bears the full loss on their behalf?

If the contract between the company and the shareholders stipulates a guarantee of capital for the shareholders, such that the company alone bears the loss, then this takes the transaction out of the realm of partnership or Mudarabah and places it under the prohibited usurious loan. However, if the contract does not include a capital guarantee, such that each party is exposed to profit and loss, then the contract is valid. And if the governmental entity bears the loss as a form of assistance without a prior condition, there is no objection. Accordingly, as long as the contract stipulates that the loss is borne solely by the governmental entity and not the shareholders, then participation in this company is not permissible.