You can use the below snippet to achieve the result.
add_action( 'wp_head', 'so_407790_add_meta_tags_to_post' );
/**
* Add category meta tags to post.
*/
function so_407790_add_meta_tags_to_post() {
// Get the current page categories.
$categories = get_the_category();
if ( ! $categories ) {
return;
}
// Category slug into list with comma separated.
$category_list = implode( ',', wp_list_pluck( $categories, 'slug' ) );
// Add meta tags to the head.
echo '<meta name="category" content="' . esc_attr( $category_list ) . '" />';
}