Questions & Answers about Mój brat jest chory, więc nie idzie do pracy.
In Polish, iść do pracy means to go to work (to the workplace), while pracować means to work (to perform work).
The sentence focuses on the fact that he is not going to his job/place of work, not on the fact that he is not working in general.
You could say …więc nie pracuje, but that would mean “…so he is not working”, which is a bit different in meaning.
Polish often uses the present tense of motion verbs (like iść) to talk about the near future.
So nie idzie do pracy can naturally mean “he is not going to work (today / tomorrow, etc.)”.
If you want to stress the future more strongly, you can use nie pójdzie do pracy (simple future), which sounds a bit more like a decision, promise, or prediction: “he will not go to work.”