Re: Customising display-fill-column-indicator-mode

[Eli Zaretskii]

> Date: Tue, 23 Aug 2022 23:36:09 +0000
> From: uzibalqa <uzibalqa@proton.me>
> Cc: help-gnu-emacs@gnu.org
> 
> > > For others, try
> > > 
> > > C-x 8 RET *VERTICAL TAB
> > 
> > 
> > To clarify: RET and TAB are keys that you press, but *VERTICAL is
> > literal text you need to type (before pressing TAB for the first
> > time).
> 
> Use *VE gives Lisp error: (error "Invalid character")

It doesn't here.  Are you sure you didn't make some typing mistake?
What version of Emacs is that?

> I would then have to use that name?  There are not many variations to choose 
> from.

Yes, there are many characters that could potentially fit.  You need
to use the character you like or want to try in the customization.