Insulation of top floor ceiling in new construction

Good day,

our shell construction is now complete and the interior finishing is approaching.

I now have the following question regarding the insulation of the top floor ceiling (the roof is already covered and fitted with an underroof + foil):

In the energy certificate, the insulation is specified as follows: gypsum board - battens - vapor barrier - insulation - OSB
[IMG width="191px" alt="Energieeinsparverordnung.jpg"]https://www.hausbau-forum.de/data/attachments/67/67457-7f595f11806696267dcea9e6fa2f8519.jpg[/IMG]

After consulting with the plasterer, at least the gypsum boards should not be installed before the plaster and screed.
Can the insulation, OSB, vapor barrier, and battens already be installed?
Or is it only sensible in this case to install the vapor barrier and the rest later? Are there problems if the insulation is pushed in later from above (I am a bit concerned that the foil could tear due to the "pressure" from above)?

[IMG width="250px" alt="Ansicht.jpg"]https://www.hausbau-forum.de/data/attachments/67/67456-30fb502ec53cc7debdf602ff0d295fed.jpg[/IMG]

The vapor barrier is laid just below the joists - correct? On the internet, the variant is more frequently seen where the foil is pulled over the joists in a wavy manner.

Best regards and many thanks for the answers

We installed the drywall sheets in front of the screed, they held up well and have dried again. But I also hammered in more Spax screws than usual. Otherwise, a panel can sometimes hang or tear out, I think.

I insulated it from below, but the carpenters said they also do it from above, putting it on the vapor barrier. That should work, seemed too easy to me ;)

I don't know about wavy, I clamped it between the rafters.