Get posts id in array by meta value and key

How to get all posts ids that has a meta key and value.

$meta_key = 'hide_rss';
$meta_value="yes";

$post_ids = array(1, 2, 3);

Use the meta_key, meta_value, and fields parameters.

Example using get_posts(): (Take note though, get_posts() ignores or doesn’t include sticky posts.)

$meta_key = 'hide_rss';
$meta_value="yes";

$post_ids = get_posts( [
    'meta_key'   => $meta_key,
    'meta_value' => $meta_value,
    'fields'     => 'ids',
] );

Or using new WP_Query():

$meta_key = 'hide_rss';
$meta_value="yes";

$q = new WP_Query();
$post_ids = $q->query( [
    'meta_key'   => $meta_key,
    'meta_value' => $meta_value,
    'fields'     => 'ids',
] );

See https://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters for other possibilities, or advanced meta query.