What is the ruling on the zakat of money deducted from salaries, to which money from the company is added as a savings fund, in cases where the amount after the increase is unknown, or it cannot be withdrawn except at the end of service, or it can be withdrawn whenever you wish?

It is not permissible to subscribe to a savings fund unless its operations are regulated by Islamic Sharia principles.

As for the Zakat on money placed in the fund: If the money is invested in impermissible ways, and you are obligated to subscribe and capable of benefiting from the amount, then the principal is subject to Zakat every year if it reaches the nisab. The profits (ill-gotten gains) should be spent on general Muslim welfare. If the money is invested in permissible ways, and you are capable of benefiting from the amount, then both the principal and the profit are subject to Zakat every year if they reach the nisab. It is not required to disburse the Zakat from the exact money held in the fund. If you are unable to withdraw the amount and benefit from it, it falls under the ruling of money that cannot be accessed or a debt owed by an insolvent person, and Zakat is paid in a different manner. Not knowing the amount of money is only conceivable if you are unable to withdraw it, and its ruling has already been explained.