Screed is too low. Are there standards for this?

One should distinguish between technical questions and execution:
- What does the planning say about the floor structure (from raw ceiling or base slab to the top edge of the finished floor)?
- What does the execution look like? What can you understand, what do you not know?

And the legal aspects:
Who planned? Who commissioned the screed layer? What does the contract say? With whom do you have which contract?

So....I did a little research...according to DIN, the height of the threshold must not exceed 25mm and this is measured from OFF WITHOUT floor covering to the top edge of the door threshold....

That still does not clarify who the cause of the error is.

'Guilt' is the absence of communication - I would sue that ;)

non-existent communication

The cause is presumably a lack of planning. However, if there is no planning at all, the respective craftsman should ask.