The `year` parameter is only used to *highlight* the current item in the list/output and it only takes effect on an archive page like date and category archives.

Try the following and visit any archive pages, and you'd see the year `2018` *option* is pre-selected:

```php
$my_archives = wp_get_archives( array(
	'type'   => 'yearly', 
	'limit'  => 10,
	'echo'   => 0,
	'year'   => '2018',
	'format' => 'option', // this outputs an <option>
) );
```

If you change the `type` to `monthly` and specified a month (e.g. `11` for November) *in addition to* the `year` parameter, like so:

```php
$my_archives = wp_get_archives( array(
	'type'     => 'monthly', 
	'limit'    => 10,
	'echo'     => 0,
	'year'     => '2018',
	'format'   => 'option',
	'monthnum' => 11,
) );
```

Then if you are on an archive page and the current item in the list matches these: 1) The year is `2018`; and 2) The month is `11` (or November); then, you'd see the item/option being pre-selected.

So that `year` parameter won't give you the results you're wanting to have; however, it is possible to achieve the results using the [`getarchives_where` hook](https://developer.wordpress.org/reference/hooks/getarchives_where/) in combination with a custom parameter, like so:

1. This should go in the theme's `functions.php` file:

    ```php
    add_filter( 'getarchives_where', function ( $where, $parsed_args ) {
    	if ( 'monthly' === $parsed_args['type'] &&
    		! empty( $parsed_args['in_year'] )
    	) {
    		$year = absint( $parsed_args['in_year'] );
    		$where .= " AND YEAR(post_date) = " . $year;
    	}
    	return $where;
    }, 10, 2 );
    ```

2. Then when you call `wp_get_archives()`, simply use the `in_year` parameter to include only the archives for a specific year: (You can the parameter name, if you want)

    ```php
    $my_archives = wp_get_archives( array(
    	'type'    => 'monthly', 
    	'limit'   => 10,
    	'echo'    => 0,
    	'in_year' => '2018', // custom parameter
    ) );
    ```

    But you can still use the standard `year` parameter to highlight/pre-select the relevant item &mdash; and if the `format` is not `option` and not `link` (which outputs a `<link>`), WordPress will add `aria-current="page"` to highlight the item.