Client GUI 2.5.16 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 (Test Version 2.5.16) according to UrBackup - Install client on Debian or Ubuntu from sources.

The GTK versions installed are:
libgtk2.0-0:
Installed: 2.24.33-2ubuntu1
Candidate: 2.24.33-2ubuntu1

libgtk-3-0:
Installed: 3.24.30-1ubuntu1
Candidate: 3.24.30-1ubuntu1

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

Situation:
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:2886): Gtk-CRITICAL **: 15:40:50.278: gtk_widget_get_scale_factor: assertion ‘GTK_IS_WIDGET (widget)’ failed

(urbackupclientgui:2886): Gtk-CRITICAL **: 15:40:51.285: gtk_widget_get_scale_factor: assertion ‘GTK_IS_WIDGET (widget)’ failed