[Aetae]

Мб так, но на самом деле хз.)

const res = [...new Set(arr.map(({date}) => {
  const match = date.match(/^\d\d\d\d-(\d\d)-(\d\d)$/);
  
  if (match) {
    const [, mm, dd] = match;
    date = `${dd}/${mm}`;
  }
  
  return `<div>${date}</div>`;
}))];