As engineersmnky commented. Changed form_with model: @order to form_with model: b fixed it!

 <tr>
      <% @orders.each do |b| %>
        <td> <%= b.recipient %></td>
        <td> <%= b.apartment %></td>
        <td><%= b.mailbox %></td>
        <td><%= b.id %></td>

    <%= form_with model: b do |form| %>


      <td><%= form.text_field :delivered, placeholder: "Entregue à" %></td>
      <td><%= form.submit placeholder: "Entregue!"%></td>
    <% end %>

</tr>
  <% end %>