Planning guest bathroom, need your tips

.. the toilet is originally 131 cm wide, and I don't think it is necessary to make the room wider.
... the shaft at the top of the plan in variant 1 is planned by the builder. What is supposed to be inside? What comes from above?

You could also place the toilet by the window and the sink at the top of the plan in the room. Then the outward-opening toilet door would be opposite the toilet and the door jamb would also be added in the space in front of the toilet.

.. originally, the WC is 131 cm wide, and I don't think it is necessary to make the room wider.

Well, depending on what is more important to you. If the shaft shortens the entire room width by 20 cm, I would also make the room a bit wider. 130 is a good dimension. Anything down to 1.15 m still works, but then it becomes quite cramped, in my opinion. However, I would definitely plan so that a 1.50 m wide wardrobe fits into the cloakroom. I would immediately cancel the wall enclosure for it on the left side of the plan, so that not a centimeter is wasted there.

The current plan now looks like this. Shaft to the right, 150x174cm, possibly 140x174cm is enough, corner toilet.
My wife wants a built-in cupboard, hence the wall enclosure.
If I remember correctly, the items for the ventilation system are supposed to go in there among other things.

I think the result is great. This way, you don’t feel claustrophobic in the toilet and the wardrobe doesn’t lose too much.

...
If I remember correctly, the things for the ventilation system are supposed to go in there, among other things.

then you are probably not completely free in the placement of the shaft?

Wow. Claustrophobia in the 2.6m² guest toilet. Our guest toilet is 1.5m²... I am always amazed ;)