That's actually the real lesson from the experiment. The detectors impart a small but real energy barrier and change the distribution pattern of the electron

Basically if you hold up a ruler to something human scale it doesn't effect the thing your measuring much. But when you are trying to measure a basketball with something the size of a gymnasium you have to really launch that fucking basketball to open a door and the door has a very noticeable affect on the trajectory of the ball.

My understanding is that they use something like polarizing filters. Both slits have the same filter, they make a diffusion pattern as the waves interfere with each other. Both slits have different filters, there's no wave interference and you get two lines.

Calling it an "observer" is maybe the most damaging name in the sciences since some douchebag decided to call the orthoganal number line "imaginary"

As far as I understand as a layman, the measurement tool doesn't really matter. Any observer needs to interact with the photon in order to observe it and so even the best experiment will always cause this kind of behavior.

With no observer: the photon, acting as a wave, passes through both slits simultaneously and on the other side of the divider, starts to interfere with itself. Where the peaks or troughs of the wave combine is where the photon is most likely to hit the screen in the back. In order to actually see this interference pattern we need to send multiple photons through. Each photon essentially lands in a random location and the pattern only reveals itself as we repeat the experiment. This is important for the next part...

With an observer: the photon still passes through both slits. However, the interaction with the observer's wave function causes the part of the photon's wave in that slit to offset in phase. In other words, the peaks and troughs are no longer in the same place. So now the interference pattern that the photon wave forms with itself still exists but, critically, it looks completely different.

Now we repeat with more photons. BUT each time you send a photon through it comes out with a different phase offset. Why? Because the outcome of the interaction with the observer is governed by quantum randommess. So every photon winds up with a different interference pattern which means that there's no consistency in where they wind up on the screen. It just looks like random noise.

At least that's what I recall from an episode of PBS Space Time.