Click vinyl and residual moisture in the subfloor, how high is the risk?

Did the screed layer really only use the drying accelerator for the bathroom? Seems a bit odd to me – normally you would try to pump everything at once. Anyway, the main thing is that the bathroom is sealed – as for the rest, I wouldn’t worry about it if I were you.

Your brother-in-law also tiled the other areas – if he had concerns, he probably would have told you in time.

Yes, my brother-in-law has absolutely no concerns. But also didn’t measure anything (presumably exactly for that reason) …

The screed for the bathroom was laid one day later - don’t ask me why, and there is also only the indication explicitly stated there.

The times and the forced drying certainly speak for me, I know that, but the house was really wet for a long time, and only through the construction dryers did it become visibly and noticeably dry very quickly.
Afterwards, the screed was certainly still uncovered for 4-8 weeks (depending on which floor), with the heating running and ventilation. Because we first wallpapered then!

So, screed in the bathroom and garage came one day later, I also assume that this was a different screed (due to moisture?), move-out invoice

Rapid screed with accelerator Rapidowitt on
on-site installed insulation with underfloor heating
60 mm thick, delivered and installed.

Regarding the tiles: they were laid by my brother-in-law, he is a tiler.

So your brother-in-law is a professional after all and knows that a CM measurement is necessary to find out or rule out whether there is still, or still too much residual moisture in the substrate in order to lay tile coverings or vinyl? Did he also fail to do that?

Yes, because he thought I had it done (which I actually always had in mind) or anyway believes it is not necessary after such a long time. But that is not the issue, because nothing has actually been measured by anyone. And ultimately that is my sole responsibility and fault :-(

you know, we also had a totally rushed birth. In the end, I was at the hospital with my wife, and the construction had to continue because everything was already terminated. They just kept working, everything was handled privately

Hello questioner.
"I know, crystal ball, but how realistic is it that there is still so much moisture in the screed now to cause damage to the construction?"
Given the long resting times of the screed, and I assume that drying conditions somehow existed in the building, I would personally sleep well!
On the one hand, the residual moisture, or rather the mixing water, in calcium sulfate screeds is chemically bound; on the other hand, this binder does not noticeably absorb moisture even at higher indoor humidity levels (unlike cement screeds).
I will intentionally set aside all other speculations about what might happen IF, because in my opinion they will not be relevant.
If the residual moisture in the substrate were too high, you would notice it visually after 6 months at the latest on floors covered with laminate flooring.
But that is just by the way!
I suspect (not unreasonably) that the Ca-screed was sufficiently dried before installation!
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Best regards and continued enjoyment in your new home: KlaRa