First of all, this would free up billions of dollars in a single year which is currently being paid to banks. In other words, this money is suspended from being used in the general economy. So forgiving student loans would put money back in the pockets of consumers. This is money which would nearly all be spent in the general economy. This would increase real profit margins, maintain and create jobs.
Obviously, this would generate sales tax revenue for municipalities and states. In addition, it would increase income tax revenue from workers who benefited from the jobs maintained and created.
This would not be a short term boost to the economy. A one time forgiveness of student loans would mean increased money in the general economy for years, even decades. Students who currently have large student loans with years to pay on them would instead be boosting the economy with the money currently going to banks for the entire length of the remaining time left on their loans. So this would not be a one-time-and-done deal. Nor would it be like tax breaks for the rich, which just went to increased profit margins and stock repurchases.