Shower installed defective + part forgotten during new construction by plumber

How should the whole thing have been properly sealed? And above all, by whom? The tiler says the plumber and vice versa. I also didn’t see any sealing collar or anything similar, neither at the bottom nor at the top. At the bottom, the structure is as follows: Wall / sealing coat / tile adhesive / tile / shower I assume that it was not sealed in between. Not even with silicone.

At the top: Wall / sealing coat / adhesive (not applied over the entire surface) for attaching the shower back panel. That was then cut open, the wall opened up to install the forgotten part. Afterwards, sealed again with tile adhesive. / sealing coat on the visible part of the wall. Then the new shower wall was placed in front, again not fully glued. The installer then wanted to install the shower. I told him it had to be sealed. Then he came around with silicone. You can also see in the picture how much silicone was needed or how wide the gap sometimes is.

Okay, I’m going to get some information regarding an expert or something similar. I would like to set a deadline, but I no longer trust the installer. I actually want someone with competence to finish it. But as silly as it sounds, I don’t want to bear the costs for it. I don’t want to be stuck with the plumber’s botched work.

Attached are some pictures.

Hi

The sealing between the wall and tile is the responsibility of the tiler.
Only regarding what I can see in the pictures:
Sealing the [Farbsets] on such a wall surface is practically impossible with the manufacturers of fittings known to me.
Possibly achievable with special components.
Nice that the client was so economical and took care of the planning and procurement of the products themselves.
One more reproach to the installer: You just have to say that this is not possible like that.

Olli