Just to confirm, I've also verified this against GTK+ Version 3.24.34:

GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.34,
 cairo version 1.16.0) of 2022-06-11

Emacs is built as follows:
./configure'
'--prefix=/home/hdiags/hdiags/spack/spack/opt/spack/linux-ubuntu20.04-skylake/gcc-11.3.0/emacs-master-tvikd2njjgseq47ywpa5zrlksnz3pylz'
'--with-x' '--with-x-toolkit=gtk' '--with-gnutls'

For avoidance of doubt, the issue still occurs when the emacs is started as:

  # No server currently running
  emacs -q --fg-daemon
  emacsclient -F '((name . "foobar") (title . "foobar-title"))'
--create-frame

xprop reports:

WM_CLASS(STRING) = "emacs", "Emacs"
WM_ICON_NAME(STRING) = "foobar"
_NET_WM_ICON_NAME(UTF8_STRING) = "foobar-title"
WM_NAME(STRING) = "foobar-title"
_NET_WM_NAME(UTF8_STRING) = "foobar-title"

Using a previous version of emacs (26.3), the same steps produce:

WM_CLASS(STRING) = "foobar", "Emacs"



On Sat, 11 Jun 2022 at 14:00, Colin Horne <colin@cdfh.org.uk> wrote:

> > I'm unable to reproduce this on the current trunk (x86_64-pc-linux-gnu,
> > GTK+ Version 3.24.31, Debian/bookworm).
> >
> > Do you still see this issue on the current trunk?
>
> I can confirm that this is still an issue on trunk.
>
> My Emacs welcome screen says:
>
> GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.29,
>  cairo version 1.16.0) of 2022-06-11
>
> Invoked as:
>
>   emacsclient -F '((name . "foobar") (title . "foobar-title"))'
> --create-frame -a ""
>
> xprop reports:
>
> WM_CLASS(STRING) = "emacs", "Emacs"
> WM_ICON_NAME(STRING) = "foobar"
> _NET_WM_ICON_NAME(UTF8_STRING) = "foobar-title"
> WM_NAME(STRING) = "foobar-title"
> _NET_WM_NAME(UTF8_STRING) = "foobar-title"
>
> This affects me in that I run simultaneous emacs instances as two
> different users and have different icons configured for the
> different users. Now that I can't change WM_CLASS, both emacs instances
> appear under the same icon under my desktop manager, which is very
> frustrating.
>
> Cheers,
>   Colin
>