Do a 48 and then use a matching fill piece for the gap

So if you use 48” vanity you’ll have 7” leftover, 3.5” on either side if vanity centered? Won‘t that just look like you couldn’t find a vanity to fit space as 3.5” is too small to do anything with? Then how do you do a BS with that little bit of open end on each side? My vote until I read a brilliant idea from someone is to stick with the wall to wall size of 55” to fill the space & to simplify the BS. Or, since it’s a powder bath, really downsize the cabinet to @ 36” or whatever that size standard cabinet is & place it against the doorway corner leaving @ 19” at toilet end IF something can be done with that amount of space. The other thing to consider with a change in cabinet size from 55” is the flooring- you’ll likely have to do new floor if you change cabinet size but I guess you know that since sounds like you’ve already removed cabinet..

Wasn’t planning on doing bs.

I do agree with @felizlady. I didn’t notice that TP holder so far from toilet - is it really or is it an Illusion created by elongated angle of photo? No backsplash? Why not? It’s not pure decorative- function is to protect wall behind faucet from water damage. Are you doing something else to glam up the powder room space? Curious about reason for redo.

How about a pedestal sink with a pretty (tall) cabinet next to the door or a small cabinet next to the toilet? You could even do a floating sink.

No toilet brush as decor, please! Ew!

No one said toilet brush as decor....they said since you have to have one in there, put it in the gap created by a shorter vanity which will hide it but will still be convenient for use.

Still ew. Keep it out of sight!

Either do a 36” free standing or use a cabinet company to create a built in something that doesn’t need giant 5” fillers on each side. Built in will be cheaper. And better.

I was considering a 36 and flush it to the right side of the wall.
Something like this. Idk such a weird space.

We tore out the floors due to some water damage so we are just running lvp throughout first floor

You can get a 54" wide vanity. Then you would just need to add a filler in the same material (same color) as the vanity.

Current vanity is dwarfing entire room.

I think you are on the right track with a 36" vanity hugged to the right side. Then you might consider a decorative shelving unit on the same wall as the toilet as I think with something taller in there it will draw the eye upward and away from the toilet when you look in the room. Just make sure you get like a 34"H vanity or taller as you want the "comfort" height in there.