You can weigh cooked or uncooked--whatever way works best for you! Two of the major things we preach here at Macrostax is sustainability and consistency. The best nutrition plan is one you can stick to, so if it's easier or more convenient for you to weigh things after you cook them, that's totally fine! Just stay consistent! The app will actually have options for cooked or raw foods! Typically the generic items are cooked. If you look for things like raw, uncooked, or dry they'll denote foods that are raw with a couple of exceptions (just ask if you’re unsure!).
That being said, weighing before you cook tends to be the most accurate because the exact amount of moisture that is lost during the cooking process can vary, depending on how you prepare your food. Also, nutrition labels typically refer to food in its dry/raw/packaged/natural state.