Is it permissible to benefit from shopping vouchers provided by the bank, knowing that they are granted in exchange for maintaining a minimum balance, otherwise a monthly fee is deducted?

A bank is either interest-based or Islamic. If it is interest-based, it is not permissible to open any account with it, as that would be assisting in usury. If it is an Islamic bank, then if the vouchers are stipulated in the contract, they are unlawful because they fall under a loan that brings benefit. However, if they are not stipulated and the bank gives them to some customers, then they are considered a permissible gift. As for the deduction when the balance is low, this has been explained previously in a fatwa.