Wasalam
May Allah bless you.
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Cashback you receive when buying something from a retailer is permissible. It is similar to receiving a discount.
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Cashback you receive from a credit card company for using their card, is also permissible. It is similar to having a debt reduction.
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Cashback you receive from banks in exchange of paying a fee, is not permissible. It is similar to buying money for money with an unequal amount. Hence, this would be classed as riba.
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Cashback you receive for keeping a certain amount in the bank accounts, or even by setting up a direct debit with them to pay the bills, are also impermissible in my opinion. In effect, the cashback is in exchange of a loan given to the bank i.e. depositing money in a bank account. In exchange of that loan, you are receiving an extra benefit which makes it impermissible.
The above might differ with @Mufti_Faraz_Adam’ opinion.
And Allah knows best!