Execute screed at different heights?

I wouldn’t do that. If you ever want to replace the crappy vinyl with something decent, the devil will get you, because, for example, parquet then won’t work.

That’s why better to look for thick vinyl and put proper impact sound insulation underneath. Then the screed can be even.

It worked great for us and the floor doesn’t mind it either.

I'll jump in here:

Today I passed on to the architect the different covering heights to be considered during the screed installation.
He then sent the following notes to the screed company:

Floorboard + WC + stairs: 9 mm, large format tile (thick adhesive bed!) + 6mm adhesive = 15mm TOTAL
har/hw r/te + wr (upper floor): 10 mm porcelain stoneware + 4mm adhesive = 14mm TOTAL
Bathroom upper floor + bathroom attic: 9 mm porcelain stoneware + 4mm = 13mm TOTAL
entire rest of the house: 12 mm parquet wide plank + 3mm adhesive = 15mm TOTAL
I assume the differences are so minimal that the SAME HEIGHT can be achieved everywhere

Is he correct regarding
a) the assessment of adhesive bed heights and
b) that the mm differences do not matter?

In my opinion, that can't be produced that precisely. It will probably come down to the screed layer installer planning for a 15mm covering height and the tile setter later ensuring identical heights with filler and adhesive.

And yes, I don't think that's the point, because just like the screed layer installer, the tile setter is not a machine. How should he manually create an adhesive bed consistently accurate to the millimeter over dozens of square meters?

Yes, he is right, same height everywhere.

Thank you +