Do MasterCard foreign exchange rates apply if a transaction is converted?

Hello there, I'm curious about how MasterCard handles foreign exchange rates when a transaction is converted. Does MasterCard apply their own foreign exchange rates to these types of transactions, or do they use some other method to determine the exchange rate? I'm interested in understanding the specifics of how this process works, so I can make informed decisions when using my card for international purchases. Could you please provide me with some insight into this matter?