If Pluto orbits at 39.5 AU, how much fainter is the reflected sunlight from a typical Oort Cloud object?

$10,000$ times fainter (factor of $100^2$)

The physical remoteness of the Oort Cloud creates an extreme light attenuation problem for direct observation. The inner edge of the Oort Cloud starts around 2,000 to 5,000 AU, meaning a typical object can be substantially farther from the Sun than Pluto (which orbits around 39.5 AU). If one assumes a typical Oort Cloud object is 100 times farther away than Pluto, the intensity of reflected sunlight follows the inverse square law. Therefore, the object would appear $100$ squared ($100^2$), resulting in it being $10,000$ times fainter. This immense drop in brightness presents a monumental technical hurdle for current telescopes trying to spot even kilometer-sized bodies there.