Final answer:
The modern aspect of the "new" art in late 18th century France was capturing the present moment. The first period of modern art to use planar recession was Realism.
Step-by-step explanation:
The concept that was modern about the "new" art of the late 18th century in France was capturing the present moment. This concept was a departure from earlier art movements, which focused on depicting idealized beauty or classical themes. The first period of modern art to use planar recession was Realism.