kaminari undefined method `total_pages'

Try to paginate with:

 List.tagged_with(params[:tag]).order(created_at: :desc).page(params[:page]).per(3)

You need to paginate both queries. I recommend something like:

def index
  if params[:tag]
    @lists = List.tagged_with(params[:tag])
  else
    @lists = List.all
  end
  @lists = @lists.order(created_at: :desc).paginate(page:params[:page], per_page: 3 )
end

Otherwise @lists will not be a pagination object when params[:tag] is nil.