Sorry, I attached the wrong patch, here's the one for the rgrep approach.

On Sat, Mar 13, 2021 at 9:46 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Allen Li <darkfeline@felesatra.moe>
> > Date: Fri, 12 Mar 2021 08:08:55 +0000
> > Cc: Juri Linkov <juri@linkov.net>, 46884@debbugs.gnu.org
> >
> > Attached patch, does this approach look good?
>
> I guess my suggestion to additionally allow specification of
> GLOBAL-ARGS interactively (via prefix arg) got voted down?
>
> > +---
> > +*** Optional 'global-args' parameter added to 'find-dired'.
> > +This allows passing find global options like -maxdepth.
>
> "find" should be in quotes: 'find'
>
> > @@ -202,6 +203,7 @@ find-dired
> >      (setq default-directory dir
> >         find-args args              ; save for next interactive call
> >         args (concat find-program " . "
> > +                       (if global-args global-args "")
>
> 'concat' knows how to handle nil arguments, so you don't need the
> empty string alternative here.  Just (if global-args global-args)
> should do.