ᐅ Shower drain installed incorrectly?

Hello,

unfortunately, I have a rather annoying problem with the shower drain in my bathroom. No water remains trapped in the trap shown in the photo, so odors from the sewer can freely enter the room through the shower drain. Any water running off just flows directly into the drain.

Could a component be missing here, or is this possibly a faulty installation?

There are two types of siphons. Usually, a hair trap/debris strainer/grid, which is black in your case, is placed under the top cover plate. Below that is the dip tube, followed by an overflow container or, in some designs, the overflow container (the actual siphon) and dip tube are combined in one piece.

It seems the second part—the overflow container (the technical term is probably different)—is missing in your setup. Normally, 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 ensures that the container always contains water and is airtight. Without the container, all the water will naturally drain away.

Here is a rough sketch:
black lines: grid
gray funnel: insert from your pictures with black gasket
red: missing container
blue lines: water flow and water level as a trap seal