By launching pkexec I got the message in xsession-errors :
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
If I launch the sofwares with sudo no messages.
I have polkit-gnome installed and launched with the xfce session.
This is the result in journalctl -f of launching pkexec thunar :
mai 16 15:29:39 Laptop polkitd: Operator of unix-session:c1 successfully authenticated as unix-user:myself to gain ONE-SHOT authorization for action org.xfce.thunar for unix-process:22411:2974190 [bash] (owned by unix-user:myself) mai 16 15:29:39 Laptop pkexec: pam_unix(polkit-1:session): session opened for user root by (uid=1000) mai 16 15:29:39 Laptop pkexec: myself: Executing command [USER=root] [TTY=/dev/pts/2] [CWD=/home/myself] [COMMAND=/usr/bin/thunar]
Any idee ?