My sewage construction in an old half-timbered house

Hello, I took over my grandfather’s old half-timbered house in 2014. In the 80s, my father renovated and rebuilt a lot. He was a craftsman and did almost everything himself. Unfortunately, he is no longer here, so I am hoping for your answers. When I took over the house, the bathroom was changed. A tiny room, which now has a walk-in shower and a toilet on the right side, with a washbasin on the left side. In the middle on the right side, the washing machine used to be installed, which had a separate drain in case of flooding. See photo. Now I have taken a closer look at this open drain. You just have to remove the grate and then you can look into a pipe about 15 cm deep. The pipe has a bottom at the end and it looks like no water can drain there. When the water runs in the shower, you can see how the shower water flows from the left into the pipe, but I don’t see any outlet. The floor cover, as far as I have seen, has a small crack. I’m now wondering, where exactly does the shower water flow to? Does anyone know these pipe systems? I am trying to attach a photo.

The water flows over the edge. When you are near the edge, it is open behind. The thing basically has a double formwork. It is supposed to catch things if they fall in and only let the water drain.

Over which edge??? The water is at most 0.5 cm high when the shower is running..... It looks like there is a big crack on the lower left side, under this strange construction on the left, where the shower wastewater flows off. I already thought the pipe was broken. I carefully pressed on the bottom of the pipe and it gave way. Help!!!! I will try to look at everything with a mirror tomorrow. Then it doesn't matter if there is a small crack in the bottom of the pipe? In other words, the bottom of the pipe is the normal drain, it is just secured so that, if necessary, hair or similar things do not get into the drain?

Martina,
Maybe you will gain more insight if you type Dusche Abfluss into Google, then look under images to see what matches yours and then follow the path further.
I just came across a YouTube video that deals with internal cleaning - very interesting and looks similar to your drain

Ypg I'll go and look for it then!!!
Thank you!