Freelancers on Upwork can be working for more than one clients at the same time. The platform doesn't limit the number of clients that a freelancer can be working for. However it is better for a freelancer to work with the number of clients that he knows he can handle at a time. Working for more than enough at a time can be very difficult. And this can even make them lose clients if they can't handle their deadlines. What do you think?