How is Zakat paid on US dollars that have reached the Nisab and on which a full year has passed, taking into consideration the instability of the dollar's exchange rate and severe fluctuations?

If the amount of dollars a person possesses reaches the value of 85 grams of pure gold or 595 grams of pure silver, and a full lunar year passes without it decreasing below the nisab, then 2.5% of it must be given as zakat (by dividing the amount by 40). The zakat can be given in dollars or its equivalent in the local currency at the time of giving the zakat.