Álvaro va a trabajar en un bar este verano.
Sometimes the English is contrived to make a point in relation ta a specific lesson. These can be quite false. To say Alvaro is working in a bar this summer means it is now summer and that is what Alvaro is doing. If asked: "What is Alvaro going to be doing this summer?" the response could well be : " He's workking in a bar this summer" meaning that is what he is going to do.
Why not give the English as " Alvaro is going to work" OR " is going to be working in a bar this summer". ?. it is less artificial and makes much more sense. (And is less irrtating)