Mountain Dew does not have antifreeze in it.
However mountain dew used to have a chemical called brominated vegetable oil, BVO which was also previously used in some other sodas.
Brominated vegetable oil does have a connection to antifreeze chemicals, which is what causes confusion.
However Brominated Vegetable Oil is a flame retardant and was used in many sodas to improve flavor and consistency although major soda brands removed it due to consumer concerns.
Antifreeze is made from ethylene glycol or propylene glycol and it's not in Mountain Dew.
Mountain Dew no longer contains brominated vegetable oil as PepsiCo removed brominated vegetable oil from their sodas around 2020 and they now use other stabilizers.