WP_Query no posts with tax_query

Your query can be simplified to this:

$products = new WP_Query([
    'post_type' => 'post',
    'show_product_on_only_premium' => 'yes',
]);

echo var_dump($products->posts);

The culprit was likely the 'operator'=>'AND', the default value is IN, so changing your original query to use IN instead of AND would also work, as would removing the operator parameter as the default is also IN

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)