The non-official Ubuntu packages for the latest emacs versions started using --with-pgtk in May. https://git.launchpad.net/~ubuntu-elisp/emacs/commit/?id=d21840558db7324543b9afa46b453b376a812720

Of interest, what's the reason for not using GDK_PROP_MODE_REPLACE when setting the property in response to a selection request?

From: Po Lu <luangruo@yahoo.com>
Sent: 27 July 2022 14:49
To: David Welch <davidwelch158@hotmail.com>
Cc: 56792-done@debbugs.gnu.org <56792-done@debbugs.gnu.org>
Subject: Re: bug#56792: 29.0.50; Emacs crashes when selecting text if xfreerdp is also running

The PGTK build does not support X11, so you should build without PGTK
enabled.  This crash is known to happen there, and will not be fixed,
since adding 300-400 lines of X specific selection code to the PGTK port
seems very irrational for a platform that it is not intended to support.

Closing, thanks.