Can one make a charity donation with a credit card and ask for change [bec he wants cash now] or is this ribbis [getting cash now paying more later]?
If he is going to give the donation regardless if he gets the change or not, then it is permitted and not ribbis. For example you wanted to donate $80 to tzedakah and asked them to make out the charge for $100 and give you $20 cash. Then we look at it, that the tzedakah received your $80 donation plus $20 for the return of the loan, and it isn’t ribbis. By the way this would be similar to when someone purchases something in a store, and charges it to his credit card but asks for some cash, as long as it is evident that the charge to the card is essentially for the purchase and the loan was only a side thing and not that the purchase was because of the loan.