Yeah... but the FBI doesn't need to write to Congress every time it decides to make an arrest. Congress delegates broad powers to the executive branch and in this case my understanding is that there were relatively few carveouts limiting what could be done with these loans. What I'm asking about is what specifically did the court reference when they said that this action was an overstepping of the branch's authority?

It was authorized by congress, specifically the heroes act. It gave the executive branch the power to "waive or modify loans" in reponse to a national emergency, and cornavirus was declared one. The law passed by congress explicitly gives Biden the power to do this. It'd a terrible ruling by the court. Not to mention the suing parties have no standing to begin with, and the suit never should have even gone forward on that basis in the first place.