Floor-to-ceiling windows on the upper floor without railing

At the inspection, there was a very simple temporary railing installed.

A temporary railing is indeed something different from a planned one that wasn’t built. ;) For our planned roof terrace, we will also have a temporary fall protection, since the terrace itself doesn’t have any fall protection yet. However, we have already installed the door leading to the terrace. So, a baby gate will be clamped in the recess in front of it. That is sufficient.

Honestly? How crazy is it to basically build a patio door to nowhere. If the window isn't fixed, it will always somehow open. And then as a complete door into the interior? Better to have it fixed at the bottom and openable at the top. It doesn't bother that much.

The problem is above all that a closed window is not enough. The "intended" use case for the check is always: an intoxicated guest stands at the window. He can certainly still open it (if it can be opened) - and thus also fall out. Therefore, some kind of mechanical protection against falling out must exist.

How crazy is it to practically build a patio door leading to nowhere.

If you have no imagination, you might think that way. For us, the deep window proves very effective – both visually and for ventilation. The sill height of about 30cm fits the room perfectly. A fall protection would spoil the beautiful view.

A crash guard would spoil the beautiful view.

It almost always does, but for that reason, you can rarely omit it. ;)

If you have no imagination, you can think like that. With us, the deep window proves itself very well

I have a lot of imagination ;) . Your window is also "only" deep. In the last house, next to the couch on the ground floor, we also had a 40cm parapet height for a view into the forest. But that is something different than a patio door on the upper floor into nowhere. In the OP's case, there are also several (all?) windows on the upper floor.