You are reading datasheets rather superficially. 120 A is the maximum continuous rating with 25° C case temperature. It's more a theoretical number for calculation purposes than anything that will be achieved in a real design.
As others have shown, trace heat dissipation can be calculated and trace width can be designed according to specification. Making a high power inverter on two-layer PCB with 35 µm copper plating might not be the best idea, but I don't want to anticipate your calculations.