Thanks so much, now it works when using that elisp function.
One thing yet:

> I am confused. I don't understand the syntax. The line "find
Documents/Org/
> -type f -iname "*.org" -exec echo " * [[file:`realpath {}`][{}]]" >
> meta-org.org \;" should be a function of its own?

That was shell command. Like in bash, dash, zsh and similar.

You mean a shell command to be executed in M-x shell-command? I did so, but
the output was

<*.org" -exec echo " * [[file:`realpath {}`][{}]]" > meta-org.org \
Thanks,
GM

El dom, 22 nov 2020 a las 21:16, Jean Louis (<bugs@gnu.support>) escribió:

> * Gerardo Moro <gerardomoro37@gmail.com> [2020-11-22 22:04]:
> > Thanks to both of you,
> >
> > find Documents/Org/ -type f -iname "*.org" -exec echo " *
> [[file:`realpath
> > {}`][{}]]" > meta-org.org \;
> >
> > Instead of "Documents/Org/" you should put there your own top
> > directory where you keep Org files.
> >
> > Then open meta-org.org
> >
> >
> > I am confused. I don't understand the syntax. The line "find
> Documents/Org/
> > -type f -iname "*.org" -exec echo " * [[file:`realpath {}`][{}]]" >
> > meta-org.org \;" should be a function of its own?
>
> That was shell command. Like in bash, dash, zsh and similar.
>
> > M-x find-dired RET Documents/Org/ RET -iname "*.org" RET
> >
> > Once I press "RET", what does -iname mean? I am new in Emacs. You mean,
> > this is just using find-dired to browse the org files?
>
> For Emacs function it is like this one here:
>
> ;; setup here your main subtree
> (setq my-org-dir "~/Documents/Org")
>
> (defun my-meta-org ()
>   "Opens my meta-org.org on the fly with hyperlinks to other Org files."
>   (interactive)
>   (let ((org-files (directory-files my-org-dir t ".org"))
>         (meta-buffer "meta-org.org"))
>     (with-temp-buffer-window meta-buffer nil nil
>       (switch-to-buffer meta-buffer)
>       (org-mode)
>       (dolist (file org-files)
>         (insert (format "- [[%s][%s]]\n" file (file-name-base file)))))))
>
> then run:
>
> M-x my-meta-org
>
>