If you change this orWhere to where that's doing and where and not or.. if you use or I would suggest you group them like this:
$articles = App\Article::with('user')
->where(function($query) use ($searchValueCat, $searchValueTag) {
$query->where("category", "LIKE", "%$searchValueCat%")
->orWhere("tag", "LIKE", "%$searchValueTag%");
})
->orderBy( 'id', $order_by_dir )
->paginate($length);