Client GUI on Ubuntu 21.10 in a Wayland session shows GTK assertion error

Hi there,
working on Ubuntu 21.10 (Default Gnome 40 Desktop Environment), I installed Urbackup Client with GUI (version 2.4.11) according to UrBackup - Install client on Debian or Ubuntu from sources

Urbackup Client GUI is working in a Wayland session and in a X11 session.

UrbackupClient GUI is working in a X11/Xorg session
UrbackupClient GUI is not working in a Wayland session. The tray icon does not show up and it yields an error message in the terminal:
(urbackupclientgui:6670): Gtk-CRITICAL **: 10:35:05.549: gtk_widget_get_scale_factor: assertion ‘GTK_IS_WIDGET (widget)’ failed

Asking @uroni for a hint or an adaptation to Wayland Display Server which is deemed to be the default Display Server on Ubuntu and perhaps some other distros.