My previous solution has the unwanted effect that it overwrites already set dates that are in the past to the current day.
Correct solution came from https://stackoverflow.com/questions/62204645/disable-dates-and-days-of-the-week-in-acf-date-picker
acf.add_filter('date_picker_args', function( args, $field ){
args['minDate'] = '0';
return args;
});