Floor outlets (supply air) under sofa and desks?

They are all flush with the floor.

So yours from #24 stands 5mm above the parquet with "sharp" edges, right?
and the version in #26 is also not flush with the floor.

An interesting variant is also one made of wood matching the floor. Basically strips with some spacing.

Yes, as already said, the grid on top can be designed however you like.

Either you pick one from the range of offers and buy a ready-made one, or you have one custom-made from wood, plastic, marble, aluminum, or a mix of materials.

Thus, you can either sink any of them into the floor, let it protrude slightly, or integrate it into the flooring in any way.

So yours from #24 stands 5mm above the parquet with "sharp" edges, right? And the version in #26 is also not flush with the floor

The fact that I (deliberately) did not recess mine completely does not mean that the option is not available.

Overall, with the Torx/Helios grates, there is a play of +/- 3cm and you can choose the final height as you like. It is similar with other manufacturers. Since the surface edge of the covering usually deviates from the plan by 1, 2, or 3 mm in most cases.

Here are more examples:

Great, thank you very much! That is even more flexible than I had hoped! This way, attaching the most extreme custom-made grids is no problem either. I can already see there is real potential in this...

After all, warm air comes out of the ventilation with heat recovery, and it then rises upwards.

Supply air preheated by heat recovery can (in the ideal limit) only be as warm as the exhaust air. In reality, the supply air is always slightly cooler than the exhaust air. Nevertheless, floor outlets work.