How to make a quantum mechanical observer at home?

This is what a typical illustration of the particle wavefunction collapse process looks like in popular science videos and articles. There is some kind of abstract eye or, as it were, an observing person who looks at a particle and after that it loses its wave properties and becomes a particle from a wave, whatever is meant by the word particle. I must say right away that this is complete nonsense, and because of such illustrations, not only people who are far from it, but even some university professors cease to understand quantum mechanics.

To dispel all the mysticism and move on to the specifics, I will talk about how to make this mystical quantum mechanical observer, so to speak, at home. In fact, it is elementary and anyone can do it. You just need to cut a ring out of cardboard or plywood, drill holes around the perimeter and pull the wires through them parallel to each other, as shown in the picture below.

The result is a wire polarizer that transmits photons only with a polarization perpendicular to the wires. A polarizer of the size shown in the picture is designed to work with RF photons. By the way, photons are unique in that they are elementary particles that can be the size of a person and even the size of a planet. It all depends on the wavelength. For example, photons with a wavelength of about 12 cm fly in a microwave. So such a wire polarizer is an opportunity to look at quantum mechanical processes with your own eyes.

If a photon flies to such a polarizer and its polarization is in a superposition of the polarizations parallel and perpendicular to the polarizer wires, then only photons with perpendicular polarization remain at the output.

For infrared photons, there are also wire polarizers, as for radio waves, only it is already much more difficult to make them at home. There are also wire polarizers for photons of visible light, only there the wavelength of photons is already less than a micrometer and it is possible to create nanometer-thick wires only by photolithography, as in the manufacture of microchips.

So the passage of a series of wires by a photon leads to the collapse of the state of the photon and, as you understand, it still has wave properties. It does not become any particle, whatever that means. Here we can say that this is the collapse of the polarization vector, this is not the collapse of the wave function responsible for the spatial probability of detecting a photon at one point or another. But the wave function of a photon in space is described by superimposing some or most often an infinite number of waves on top of each other. And when the wave function collapses, one of these waves is chosen in theory, and in practice, a certain group of waves or some part of the spectrum with a continuous spectrum. So after the collapse of the wave function, another wave is obtained, and not some mythical particle that does not have wave properties.

So why, when describing a double-slit experiment, is it said that after observation, a photon or electron begins to behave like a particle, and not like a wave?

As you understand from the example with a wire polarizer, for the collapse of the wave function of the mythical eye, it is not enough, as in the picture above. To find out which slit a particle passes through, it needs to collide with another particle or group of particles. After the collision, the wave function of the particle already turns out to be coming from only one slit, and not from two. Therefore, on the screen behind the slit, no addition of alternative paths of the particle, no interference is obtained any more. Although, by changing, for example, the wavelength of the measuring or, so to speak, observing particles, it is possible to make the wave function of a particle passing through the slits go mostly through one slit and a little through the other. Then there will be partial interference. Not as clear as if there was no measurement at all.

So if you look at the mathematics of quantum mechanics, then nowhere can you find the loss of the wave properties of particles in any process. And speaking about the fact that an elementary particle is a particle or a wave, we can say that it is always a wave, but a very unusual wave