Lag is created by animation. With disable you disable just the collapsible animation and you see the Object opened.
here the code:
if you want keep the animation you can try “icon-toggle” option. The performance wille be better but, for me, not enough. In fact i disable whole animation in my applications.<q-collapsible opened icon-toggle icon="shopping_cart" label="Third"> <div> Content </div> </q-collapsible>