When is it a construction defect? A 10 cm wall was incorrectly placed

... my idea would also have been to install a smaller door. Instead of an 89, just install a 78 door.

This may result in the problem of whether the tub no longer fits through the narrower door and around the corners?

In my perception, a 10cm error is already relevant for approval.

What can I do and what rights do I have.

You can first of all fulfill your obligation as a questioner by illustrating the question with plans!

my thoughts on this:

Wood has advantages and disadvantages. One of the advantages is that you can approach it with a chainsaw and reshape it (unlike with stone or concrete). I would consider whether it would be possible to let the tub "disappear into the wall" by 10 cm. Either the "remaining wall" would then be very thin, or a step would be created in the adjacent room (which might be useful for something). (a drawing is actually very useful for such considerations :)) my experience: It often happens that correcting a mistake results in a better outcome than it would have been without the mistake.

Since it is a timber frame house

And precisely with these buildings, the positions are specified down to the millimeter.
So I really don't understand the wrong positions.
Who botched this here?

Question I am asking myself again: can I claim something money-wise because of the 10 cm

It remains unclear what your priority is. Do you prefer money or a bathtub you can "fit into"? Your approach depends on that. Leave out the problems and your frustration for now, they only get in the way of finding a goal. Your construction partner, who has confirmed the mistake, can only find a suitable solution with you if your goal is clear. All the questions about how this happened are of no help whatsoever. The only relevant question is how it should be, and that you specify. And once again for clarity: not how something should be done now, but what result you specify.

The room has become 10cm smaller because of this and I therefore have a larger hallway.

Show me the plan of the upper floor, that is the bathroom and hallway. Maybe another idea will come up related to the ones you mentioned.

My idea was also to install a smaller door. Instead of an 89 cm door, to install a 78 cm door.

One could also have a door that opens outwards. I now don’t understand why nothing can be changed with timber frame construction. (Or is it a solid wood house?)

The plan was to install a 1.70m bathtub there, which unfortunately no longer fits because the door would now hit the tub. I just wonder how I should proceed. A 1.60m bathtub is out of the question for me because unfortunately I don’t fit in there.

Since I myself would never install a narrow 170cm tub (apartment construction) in a single-family house at a height of 165cm, I looked into bathtubs for our terraced house bathroom renovation back then. We ordered an (inner) egg-shaped tub with a leg width of 90 x 160, something like that. It was 5 cm higher, which is quite a lot. There are some dimensions that are quite space-saving on the outside, but so that there is plenty of space inside where it is needed (more arm area, less foot area). These tubs are more expensive; the additional cost should be covered by the builder’s insurance. And if you build one more time, my tip: in my opinion, a tub needs some shelf space on the left, right and/or back, i.e., platforms. Planned with 180cm in length and 2.40m width you are in a good spot. That compensates for few corrections and provides comfort.