Insulate the top floor ceiling without a vapor barrier

You are overthinking it.
Normal mineral wool is just as vapor-permeable and usually better insulating and cheaper than the wood wool.
Basically, the company says the same thing as I do, as long as the cold roof remains, there is no need to make a science out of it.

Yes, I also think we should do it that way, the steam can simply escape everywhere.

We will see.

I would like to thank everyone who has contributed.

I'm asking again out of interest

Without a vapor barrier, moisture enters the insulation, that is where the dew point is. The vapor condenses and water is in the insulation. If everything is open to the outside, this effect does not occur? Is the dew point bypassed there, that can't be, right?

I am of the opinion that you are right there, so yes, moisture gets into the insulation and probably stays there.

But I think (I am not a professional and am just thinking aloud) that if the roof is open and you have insulation that can store and release moisture, nothing will happen.

I believe it depends on the insulation.

If you have insulation that cannot handle that, everything is rubbish and ineffective.

I also think that if the roof were closed (foil in front or something else), then insulation that stores and releases moisture would be nonsense, because it would then be like a wet sponge.

Don't hit me, that's how I imagine it. !!!

Here is my shortened answer

So, "Yes, without a vapor barrier, moisture gets into the insulation whether the roof is open or not."

Here you just have to try to get rid of it again and that probably only works with an open roof and insulation that does not get damaged.

I'm asking again out of interest

Without a vapor barrier, moisture gets into the insulation, that is where the dew point is. The vapor condenses and water is in the insulation. If everything is open to the outside now, does this effect not occur?
The dew point is bypassed there, it can't be, right?

The first part is correct, of course moisture gets in, but it just goes out again. The dew point in this case is not in the insulation.
Why exactly this is so I can't say, probably because it dries out too quickly, but the dew point is also shown with the U-value calculator if it lies within the envelope.
In that respect, I may once again refer to my schematically probably fitting little picture, there is no dew point in the insulation.

Yes, I have already seen that and it just seemed strange to me that there is no dew point. But well, if it works like that, you can put it aside for now and take care of other things.^^