Wordpress how to filter posts basing on custom field in certain post type

You could use the following conditions to alter the query:

• is_single^Docs function to check whether the query is for an existing single post.

AND

• Using get('post_type') method on the "$query" variable.

add_action('pre_get_posts', 'filter_by_user', 9998);

function filter_by_user($query)
{
    if (
        is_single()
        &&
        'customer_bill' == $query->get('post_type')
       ) 
    {

        $user = get_current_user_id();

        $meta_query = $meta_query ?: [];

        $meta_query[] = [
            'key'     => 'id_customerJK',
            'value'   => $user,
            'compare' => 'LIKE',
        ];

        $query->set('meta_query', $meta_query);
    }
}

Try :

if ( is_singular('customer_bill') ) {
// Your Code

or

if ( ! is_singular('customer_bill') ) {
    return;
}
// Your Code