[fori]

Сделал версию на array.map

let countries = [
  {
    iso: "ca",
    flag: "<svg></svg>"
  },
  {
    iso: "us"
  },
  {
    iso: "an"
  }
];

async function optimizeSVG(str) {
  return str;
}

async function filterCountries() {
  const countriesToIgnore = ['an'];

  let result = await Promise.all(countries.map(async (country) => {
    if (!countriesToIgnore.includes(country.iso)) {
      let flag = await optimizeSVG(country.flag);
      return [country.iso, flag || 'noflag'];
    }
  }));

  result = result.filter(Boolean);
  console.log(result);
}

filterCountries();

но можно ли без result = result.filter(Boolean);