Here’s what I’m thinking as far as the walk-in shower for inspiration.

Do you use the tub & is there another tub in another bath room?

I have another tub. I do like bathing, but the other bathtub would suffice.

Here are some measurements. The entry door is standard, and there isn’t much of a wall by the WC. Hope that’s helpful.

I’d love a linen closet, but that might need to go in the walk-in closet

If you have another bathtub, i would do a larger shower for sure.

Looks like there’s room to make the shower deeper. I don’t think there’s a great way to enclose those windows in a shower, anyway.

Depending on how extensive you want to go, I'd think about moving the vanity into the space of the tub and shower (easier to work with a window than having it in the shower) and put the shower closer to the area where the vanity is. If the door could be moved to the right, you'd have a huge area to work with, but even if it has to remain, I think you could put a good size shower in that space. Maybe have your linen closet between the wall by the door and the wall of the new shower.

We do think removing the carpet is a great idea. Perhaps look at some bathroom inspiration before you proceed. Here is a bathroom we did which might interest you:

Contemporary Spa Inspired Bath · More Info

Contemporary Spa Inspired Bath · More Info