You can never have two independent, isolated pathways.
It’s called the tunneling effect.
It can tunnel through time or space or energy barriers. Not every time, but enough times to make you throw out the baby with the bathwater.
While that is true for some barriers, I believe it is possible to erect a barrier, e.g., to block photons. Without a barrier to block photons, how do you make a slit, or differentiate a one-slit "barrier" from a two-slit, etc.?
In Young's experiment, observing the wave nature of a photon depends on a single photon having access to more than one slit. When a single photon has access to one slit, a bell-curve pattern results. My remark is that one could run two of those "one photon at a time, one slit" generators and superimpose the bell-curves. What is the result?