I just got back. If it is more cost-effective to spend a card with UnionPay there, UnionPay is very common there. Thai baht will be brushed directly according to the exchange rate of the day, and the bank said that there is no handling fee for credit card consumption. Many ATMs there can also withdraw cash, which is also calculated according to the exchange rate of the day, but there is a handling fee. Travel agencies or some hotels there can also exchange Thai baht, but the exchange rate will be lower and not cost-effective.

I suggest you call the bank where your card is located, and they will tell you in detail after consultation.

Actually, I think it's best to change enough money. Thai baht can't stand flowers, and they spend quickly.