Insulation under screed in old building renovation with underfloor heating - experiences?

The offer has not yet been signed. To be fair, I must say that I did not give the heating engineer any specific instructions and I also assume that such points could still be changed.

The monetary effort for vacuum insulation panels is probably in no relation to the possible energy savings.

Unfortunately, I have that feeling with most energy-saving measures, especially in old building renovations. Saving energy is a luxury. Therefore, for the time being, a gas boiler will remain.

Is the underfloor heating system panel worthwhile instead of the biofiber perforated panel, and maybe 30mm XPS/EPS instead of the 20-5 mineral fiber impact sound insulation on the ground floor?

Insulating an uninsulated floor to an unheated basement (whether from above and/or below) is likely to make financial sense in any case. Here we are talking about costs of <30€/m² (even less if you do it yourself).

Vacuum insulation panels all in are certainly well over >100€/m². As far as I can tell, this is generally a very complex matter because, logically, you cannot cut the panels. So it must be precisely planned in advance and produced according to your needs.

Any kind of "special system" for underfloor heating will always end up being more expensive than the classic variant with wet screed. With about 10cm floor construction, I personally see no need for that. Approximately 2cm for the pipes, plus 3.5 - 4.5 cm coverage by the screed and 1.5 - 2.0 cm for the covering, leaves you 20-30mm for insulation under the screed. Cost here in our "countryside" about ~30€/m² for underfloor heating and another 15€ for the screed plus the floor covering.

If you now choose 30mm PUR as material and can spare another 60mm under the basement ceiling, you will achieve a total U-value of < 0.25 and could even have the measure subsidized by the KFW.

Upstairs you then take EPS impact sound insulation in the maximum possible thickness; it doesn’t get cheaper.

The package from the offer seems to come from the ecological corner to me. Whoever has the money for it and wants to atone for the X5 in the driveway should take it. In my opinion, it does not offer added value.

Unfortunately, I have that feeling with most energy-saving measures, especially in old building renovations. Saving energy is a luxury. Therefore, it will remain with a gas boiler for the time being.

Investments in energy saving are not a luxury but often pay off. The most efficient measures should always be carried out first. Those who want to exploit everything will of course end up paying, but in a 1960s building there is usually a lot of potential for investments that pay for themselves after 3-10 years.

Switching from a gas boiler to something else just because it is trendy (heat pump?) will probably hardly or not at all pay off in your case.

Is the underfloor heating system panel worthwhile instead of the biofiber perforated panel, and instead of the 20-5 mineral fiber impact sound insulation on the ground floor maybe 30mm XPS/EPS?

A "special system" however designed for underfloor heating will always end up being more expensive than the classic variant with wet screed

As Dr Hix already said: Underfloor heating is not really an investment in energy saving but for increasing comfort and it also costs more. Without underfloor heating, you can lay wooden floorboards on joists with insulation in between or insulation + dry screed + covering.
For underfloor heating, there are various approaches; not all are more expensive and many are simpler than the new build variant with tack boards and poured screed. A dry system has a lower build-up height than poured screed and thus enables better insulation downwards.
Suggestion for own labor: Fully glue construction boards (cement-coated, fiberglass-reinforced XPS boards from e.g. WEDI or Jackodur), mill channels for underfloor heating, lay pipes, fill in and cover with flooring (parquet or tiles). 8 cm insulation, cheap and fast. There are also dry systems that, for example, simply work wooden floorboards into the top layer of insulation between the joists. Also maximum insulation and quickly finished.

PS: On the ground floor, if there is only the basement underneath, impact sound insulation is not necessary.