I don't know if it will help, but I found workaround to capture X-clipboard.

Since %x doesn't work with daemon, I used %i and passed X-clipboard's
content using xsel. Like,

xdg-open "org-protocol://capture?template=h&body=`xsel`"

On Mon, Feb 22, 2021, 8:25 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Parvesh Monu <parvesh.dhullmonu@gmail.com> writes:
>
> > I have this template which captures clipboard content in file. It works
> fine when
> > emacsclient is running, but if no client is running then server adds
> empty entry.
> >
> > (add-to-list 'org-capture-templates
> >        '("x" "Clips" entry (file+headline "/home/user/desktop/clips"
> "Clips")
> >          "** %x" :immediate-finish t :prepend t))
>
> I'm not quite sure I understand you correctly here -- but I think you're
> saying that if you start "emacs --daemon", then that daemonised Emacs
> can't communicate with the X clipboard?
>
> I'm not sure, but doesn't that sound quite natural?  If you don't have
> an X window open, then you can't talk to the X server, so you can't
> access the clipboard, either.
>
> I don't know how Org is talking to the clipboard, though.  Anybody?
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no
>