Underfloor heating beneath floorboards

Concealed screws in the spring at a 45-degree angle. There are special ones including a drill tip. For example, Assy-Plus floor screws

Sensible. Fine.

I'll throw something in... You don't want radiators, nice real floorboards, and pleasant radiant heat? Just google [Sockelleistenheizung], it's cheap and effective.

Do what you want, my brother, master craftsman painter, clearly says, floorboards and FHZ are energy waste to the power of three. The eco-freak lives on wood and just pushes the gas through the burner and the CO2 into the air, but we do have wood, not PVC in the hut. Hypocrisy.

It is feasible as many have already described here, but it is not sensible, because the operating costs will (to put it exaggeratedly) be at the level of an old building.

Do what you want, my brother, master craftsman painter, clearly says, floorboards and FHZ are energy waste to the third power.

Sure, the same efficiency as glued tiles will not be allowed by a 20mm solid wood floor with the FHZ. But glued parquet doesn't either. Due to the material.
"To the third power" sounds like there are several orders of magnitude between them. I can't see that in the most recently surfaced construction. If it is well done, the biggest loss is due to the material (wood is simply not such a good heat conductor). Whether glued or not doesn't change that at first.

I don't see where the energy waste is supposed to come from. The challenge is purely of a craftsmanship nature: the insulation surrounding the heating pipes must be done well and the contact from below to the floorboards (or heat-conducting plates) must be consistently tight.
But then it works, why shouldn't it?

I can't think of any physical reason. If master craftsmen do not do it masterfully enough and the loss lies in that, poor thermodynamics can't be blamed...

It is feasible as already described by many here, but it is not sensible, because the operating costs will (exaggeratedly speaking) be at the level of an old building.

That is exactly what I formulated much earlier with my message. Surprisingly, this has not been understood until now... In the meantime, it was said that it would work/be feasible. Of course it is. But it is not sensible.