Exclude Specific Categories from RSS Feed on WordPress

<?php
/**
 * Exclude a category or multiple categories from the feeds.
 * If you want to exclude multiple categories, use a comma-separated list: "-15, -5, -6".
 * Make sure to prefix the category id(s) with a minus "-".
 *
 * @param WP_Query $query The query.
 */
function wpcode_snippets_exclude_feed_category( $query ) {
    if ( $query->is_feed ) {
        // Replace 15 with the desired category id you want to exclude.
        $query->set( 'cat', '-15' );
    }
}

add_action( 'pre_get_posts', 'wpcode_snippets_exclude_feed_category' );