Yeah, there is no good reason to believe that, and it doesn't even make mathematical sense. Those kinds of popsci articles are entirely misleading as to what is actually measured.

If a photon in the double-slit experiment really spreads out as a wave to "propagate through both slits at once," then you would describe the particle mathematically as a field in physical space, assigning M sets of numbers to each possible place in physical space to represent the properties of the wave at that location. If you have N particles, you'd need N fields, and since each field would need M numbers, you would need NM total numbers.

For 1 particle, the wavefunction in its position basis is also of size M, so you can assign each element of the wavefunction to a position in physical space, and then show a fancy visualization of the particle spreading out as a wave, taking all possible paths, going through both slits at once.

But the number of elements in the wavefunction scales by N^M, not NM. So this visualization quickly stops making mathematical sense as you add more and more particles to the system. Given 3 particles and 2 locations they can be in, that's NM=6 and N^M=8, so there is no consistent way to break apart the wavefunction into assignments of waves in physical space.

Mathematically, the idea of waves propagating through space like this makes no sense. If you actually look at what is measured in the studies of the papers cited, they always just measure particles, but then, over very large samples, the particles form wave-like patterns.

That would be like saying because a collection of H2O molecules can form waves on the ocean, then therefore a single H2O water molecule is a wave... it's nonsense. The wave is a property of the ensemble statistics, it is not a property of the individual system. The individual particle is just a particle. The wave is only observed over its ensemble statistics.

The only "wave-like" thing about particles is that, as far as we know, their behavior has a fundamental element of randomness to them, and so we have to describe them using ensemble statistics, and their ensemble statistics have certain wave-like properties. But that does not prove a single particle is a wave, that it spreads out and takes "all possible paths at once." There is no evidence of that. No experiment has ever caught a particle in two places at once. They always find it in a specific place, and the only thing that is in more than one place at a time is the ensemble statistics!