Is it permissible to withdraw money from the bank to trade it in the black currency market, knowing that the country is suffering from illiquidity and high prices, and is it permissible to exploit the price difference between cash deposits and actual cash?

There is no objection to trading currencies and benefiting from the difference in price between deposit and cash exchange, provided that the rulings of legitimate exchange are adhered to, in terms of mutual possession (qabdh) and absence of deferment, and the absence of cheating, deception, or exploitation of one's banking position without permission, and that the state does not prohibit this trade (black market) for a recognized public interest.