Is it permissible to pay zakat and sadaqa to an organization that returns a portion of the donated amount to the donor (representing a tax deduction), such that the amount deducted from the donor is less than the original amount paid?

The entire zakat money must be disbursed completely among the eight legitimate categories mentioned in the Quran, and it is not permissible for the zakat payer to take back any part of their zakat. However, if what is returned to you by the state is a reduction of the taxes owed by you, because you paid your zakat to charitable organizations, then this refunded money is yours and does not affect the zakat, because it is not a return of zakat but rather a tax exemption procedure.