31 U.S.C. 5103 https://www.law.cornell.edu/uscode/text/31/5103) says “United States coins and currency (including Federal reserve notes and circulating notes of Federal reserve banks and national banks) are legal tender for all debts, public charges, taxes, and dues. Foreign gold or silver coins are not legal tender for debts.”
It’s not legal tender for just court judgments, but all debts, public charges, taxes, and dues.