FWIW, it remains possible to use some at least some mainland China-issued UnionPay cards at Iranian ATMs. In particular, Bank of Kunlun still processes transactions with Iran.

Obviously, not useful if you don't have a chance to set up an account while in China, but something to look into if you travel to Iran frequently and are wary of carrying large amounts of cash. Of important note is that you can't make international wires in, as Bank of Kunlun is itself sanctioned by the US, so you'd need to transfer funds via another Chinese bank.