The dimensions for the door/window/wall are still missing.
Regarding the bathtub: it does not need a pre-wall because it can receive its supply and drainage connections from the floor.
I would also let go of fixed measurements. A shower doesn't have to be square or at least one meter on both sides; it needs comfortable dimensions. But if the desired measurements fit, of course, you take them.
12sqm is already large but can still be insufficient if the window and door are wrongly positioned.
The position of the door here has the disadvantage that you can't help but bump into something when you go through the door (it's always the staircase's fault! If it's placed wrongly, something else gets stuck). But they will probably reduce the staircase opening at the bottom a bit; then you'll get another 30cm.
I would orient myself on V2, but put the glass shower door forward. The bathtub can be positioned a bit closer to the shower and set on pedestals on the left and right.
A 180x80 bathtub is completely sufficient for 2 people — too large consumes too much water. The shower/bathtub line is important for me to maintain, best achieved with a pedestal or tile shapes.