Shower drain installed incorrectly?

Hello,

unfortunately I have a small but big problem with my shower drain in the bathroom. No water remains in the seal shown in the photo, so the smell from the sewer enters the interior unobstructed through the shower drain. Running off water goes directly into the drain.

Is it perhaps just a missing part here or could it be a faulty installation?

The siphons come in two versions. Usually, on top of the cover plate is the hair trap/debris trap/strainer, in your case in black. Below that follows the dip tube and then an overflow container or the overflow container (actual siphon) and dip tube are in one piece.

In your case, the second part, the overflow container (the technical term is probably different), seems to be missing. Normally, the water flows through the pipe into a container that surrounds the downward-facing white pipe and has a slot at the top where the water overflows. This causes water to always stand in this container, and the whole thing is airtight sealed. Without the container, of course, everything runs away.

Here is a amateurish sketch:
black lines: grid
gray funnel: insert in your pictures with black seal
red: missing container
blue lines: path of the water and water level as a water trap