Praise be to Allah.
There is nothing wrong with working in the mint, and this work has nothing to do with the transactions of the riba-based banks. The people’s need for this currency is obvious to everyone, as it has become essential to their lives. Production of this currency is connected to the strength or weakness of the local economy, and the relationship between the mint and the central bank is not one of transactions, rather it issues orders to print a certain amount according to the fluctuations in the foreign currency reserve and the economy.
And Allaah knows best.