Let me say once more what for quantum particles wave-particle duality means.
When quantum mechanical particles interact , they give a footprint of one point, within the measurement errors and the Heisenberg uncertainty principle. That is why they are called "particles".
Here is the double slit one electron at a time experiment.
Electron buildup over time
Note the random pattern becoming an interference one, with the accumulation of the distribution of different electrons with the same energy and through the same boundary conditions. It is obvious that an interference pattern exists. This accumulation is a probability distribution for each electron to be found at the (x,y) of the screen. What is waving is the probability, i.e. the solutions of the quantum mechanical equation, the $Ψ^*Ψ$ for the experiment "electron scattering off two slits given distance and given width". That is why it is called a "wavefunction", it is a solution of a wave differential equation.
Again note, the individual electron is not spread all over the screen. The accumulation of electrons displays interference patterns expected by waves.
When "a which way detector" is put after the slits, one is changing the boundary conditions of the experiment and a different wavefunction solution applies. This is seen in this experiment
Overall, the results suggest that the type of scattering an electron undergoes determines the mark it leaves on the back wall, and that a detector at one of the slits can change the type of scattering. The physicists concluded that, while elastically scattered electrons can cause an interference pattern, the inelastically scattered electrons do not contribute to the interference process.
A rule of thumb for the so much abused word "duality" is that when quantum elementary particles interact, they interact as point particles, with a probability following the wave equation solutions for the particular experimental setup.
Here is a bubble chamber picture of an electron
Beam tracks are $K^-$ at $4.2 GeV/c$ and one of them hits a hydrogen atom with enough momentum to expel an energetic electron, seen to lose energy as it ionizes hydrogen atoms while turning in the magnetic field (B, perpendicular to the picture). All the dots making the tracks are the usual small energy transfers that lead to ionization and allows to see the charged tracks.
There is no spread of the $K^-$ all over the place, they behave like classical particles ( until they undergo a deep inelastice interaction with a proton, when a lot of tracks can be produced. See the link for more . It is the accumulation of $K^-p$ that allows to study the quantum mechanical behavior/probabilities .)