The one-two punch of the photoelectric effect and the double slit experiment (the classic first two labs of QM) force you to accept that photons behave both like waves, and like particles.
This is the reason for statistical interpretation of QM that states that a wave function is just a way to calculate probability with no inherent meaning.
So wave-particle duality is just an artifact of Copenhagen interpretation of QM, not something that one can observe. What one clearly observes that photons travel through a region where they should not classically be and never appear in the region where they should be classically.
Note that even classically waves does not exist as they are just an artifact of motion of collection of molecules that on average can be described by wave-like equations.
The same could be said of the entirely unsurprising many-photon case. The individual photons aren't demonstrating the interference pattern, just the "big enough sequence of single photon measurements". Again, that's not the interesting part of the double slit experiment. We're perfectly used to the concept of a collection of many interacting particles having wave-like properties.
The double slit experiment has non-interacting photons demonstrating wave-like properties.