Although diffraction and interference are mostly referred to phenomena of light, I would like to start with water waves.
The problem is best observed at the surface between water and air. In a water channel with vertical walls, a plane water wave travels almost undisturbed. A plane wave is not weakened by lateral propagation at the ends of the wave. We see a pure transverse wave in which there is a pure upward and downward movement of the water molecules along with density changes.
As soon as the channel becomes abruptly wider, the wave ends on the left and right will diverge in a circular pattern, with their amplitude weakening.
If the experiment changes so that the channel becomes a slit, you still have the same result. What is decisive is not what happens in front of the slit to the right and left of it - this part of the wave is simply reflected - but what happens after the slit in the previously calm water - the wave spreads out in a circle to the left and right of the slit. This phenomenon is called diffraction of water waves.
When two water waves meet, their amplitudes can strengthen (the molecules move in the same direction at that point and time) or weaken. This phenomenon is called interference of water waves.
Things happen a little differently with particle streams. It is irrelevant whether we are dealing with electromagnetic radiation or electrons.
Even when two currents meet head-on, nothing usually happens. However, when the intensity of the currents increases, particles can collide. The electrons then change their direction, they are scattered.
This behaviour does not change when the particle currents are emitted in waves, i.e. for EM radiation as a radio wave. The waves penetrate each other effortlessly. Since information is usually imprinted on such waves, the two pieces of information may overlap in the case of a receiver. However, this is by no means interference in our sense.
This also makes it clear that the term interference for particle streams behind edges is only a common name. In reality, however, it is a matter of deflections aka diffraction of the particles at the edges and an intensity distribution behind the edges.