Are the monthly deductions from the salary, with fixed percentages added by the institution, which are then invested and distributed as variable profits, and in the event of a one-time loss, considered usurious interest?

It is permissible for the employer to deduct a portion of the employee's salary with their consent to invest it, with the addition of another sum from the employer, provided that the investment is in permissible ventures, and that the employee's capital is exposed to profit and loss, and that their share of the profit is a common percentage. If any of these conditions are not met, then any amount exceeding the deducted sum and the gift is considered usurious interest, and it is not permissible to enter into it voluntarily. However, if it is obligatory, the employee is only entitled to their capital (the deducted amount and the gift), and the surplus should be spent on general Muslim welfare.