( مُتَبَّرٌ ) (destroyed): meaning doomed.

( وَبَاطِلٌ مَّا كَانُوا يَعْمَلُونَ ) (and worthless is whatever they were doing): What they did was void, destructive, and utterly worthless, and it is a reprehensible act. This ignorant and ungrateful manner was the first thing they did after being blessed and rescued by Allah (swt).

The scene then moves on to the conversation that took place between Prophet Moses (PBUH) and the Children of Israel when they asked him to make them a god: