Using a combination of ... , Set , .map() and .sort(). This can be done in one line.

... -> destructures array into individual items.

new Set() -> make a set out of the new items.

map() -> runs a loop and map the array into a new one.

split() -> breaks a string into array.

sort() -> sorts an array.

var array1 = ['9/2022','7/2020','11/2021','12/2020','2/2020','4/2021','10/2021'];

console.log([...new Set(array1.map(x => x.split('/')[1]))].sort());

You can easily achieve this result using Set and map

var array1 = [
  "9/2022",
  "7/2020",
  "11/2021",
  "12/2020",
  "2/2020",
  "4/2021",
  "10/2021",
];

const result = [...new Set(array1.map((s) => s.split("/")[1]))].sort();

console.log(result);

You can map to get only the years, and then sort the results. Then you instantiate a Set which removes all duplicate entries.

new Set(['9/2022','7/2020','11/2021','12/2020','2/2020','4/2021','10/2021']
  .map(dateAsString => dateAsString.split('/')[1])
  .sort());