Assalamu alaykum, Shaykh. A financial app offers 5% cashback on SPENDING if I keep $1 million deposited with them; lower balances earn less cashback. Is this permissible, or is the increased cashback a benefit from lending them money and therefore riba? JazakAllahu khayran.

If the money is held in a current account, it is a loan to them, and as the scholars have said the lender may not take any gift or benefit from the borrower, so cashback that rises with your balance is a benefit drawn from the loan, which is riba. If it is a genuine sharia investment account where you share in profit and loss, this does not apply.