Created attachment 7514 Use 'gdk_screen_is_composited' with Gtk3 The 'gtk_widget_is_composited' function is deprecated with Gtk >= 3.22, we need to use 'gdk_screen_is_composited'. Patch fixes this issue.
Olivier Duchateau referenced this bugreport in commit 96b8a42da2134089b616569d6878735fe81d9cca Use 'gdk_screen_is_composited' with Gtk3 (Bug #14128) https://git.xfce.org/xfce/xfce4-panel/commit?id=96b8a42da2134089b616569d6878735fe81d9cca
Thanks, pushed!