Is buying currency with an uncovered card, then immediately paying the withdrawn amount—including the fixed fees—to the bank, nullifying the condition of the loan and making the card as if it were covered, and thus not considering this transaction unlawful?

If the card is not covered, the bank is not permitted to charge fees exceeding the actual cost, because cash withdrawal is considered a loan from the bank to the customer, and any stipulated increase is considered usury (riba). It is forbidden to purchase gold, silver, and currencies with an uncovered card.

However, if you deposit sufficient balance in the uncovered card, it takes the ruling of a covered card, and the bank is permitted to take an 8% charge, even if it exceeds the actual cost, and there is no harm in purchasing currencies with it.

But if the card is uncovered and does not have sufficient balance, and then you make a purchase with it and pay the bank immediately, its ruling does not change, as you would have borrowed from the bank, and it is not permissible to pay an 8% charge if it exceeds the actual cost, as this is considered usury.