Shower bath (2.5 sqm) and full bath (11.6 sqm) floor plans included

The question is rather whether you really want to impose that on your guests? It is possible, but it’s not nice.

Here is our guest WC with a shower.
It is quite usable and should definitely be equipped with a shower. That is also necessary in order not to have to drag the dirty ones through the whole house first. In even less space, the shower won't work in my opinion.

The shower is 80x80 flush tiled. Anything else would be disturbing. As a partition wall, (not yet present) a folding door on both sides makes sense.

The only disadvantage of the bathroom: My wife wanted a 101 cm door, which would hit the knee when sitting on the pot.

I would have the door open outward then... if someone collapses in the small room, otherwise you can't even get to them.

... have you ever showered in a 75x75 cm shower?

I had a 70x70 shower on vacation: doable. Emergency shower. It helped my husband that the curtain is "stretchable" outward.

But the dear toilet is used every day and should be built according to current standards. What use is a shower for occasional use if the rest does not make you happy at all. The same applies for this washbasin described below... we had a similarly small one in the townhouse. As a result, we washed our hands in the kitchen.

Dimensions an unbelievable 36x18. With a door opening outwards, it would look like this with an 80 cm shower:

1.46 meters is a shell construction measurement. Means: Plaster 3-4 cm... tiles including adhesive 2-3 cm... we are at 1.40. 70 cm shower, 70 remain for the toilet. It is 35 cm wide, then 17 cm on left and right each. Kerstin already suggested it: Try cleaning your backside. And then grandpa came ...

or a pregnant friend or just someone overweight... I probably wouldn't dare to use the bathroom at your place then. Well
look here

baeder-seelig.de/minibaeder-Ideen

this is a shower bathroom of 1.5 sqm. Nice is something else, but theoretically doable. For slim people.

Here a space is being theorized that would be a total disaster in practice. Quite real in daily use, not in the hypothetical case of a collapsing flabby cheek.