> 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