Bathroom layout 8.5 m², how can it be improved?

I have a similar problem between shower and tub as well.

What is the extra cost for such a panel that sits on the tub wall? It doesn't look complicated in pictures on Google. Basically just a panel and a door sized to fit.

Alternatively, how about installing a fixed wall at shower height? It won't be as bright in the shower, but it provides better privacy.

Solid wall. Tiled. Finished. Or solid wall from the catering sector for small systems. Kemlit or similar. Also works.

Then you didn't know yet that many GCs (most?) have completely removed all shower enclosures from their construction specifications.

Yes. It's not just since yesterday. Building was expensive even 6 years ago!

But I agree with my predecessors :)

Then your statement that it is not an optional extra makes no sense?