viyoriya Thank you very much for your patience and help.
Running
cd /usr/share/applications
sudo cp examplefile examplefile.desktop
did not work. It gave the output: cp: cannot stat 'examplefile': No such file or directory
Running "sudo nautilus" and then renaming the file through GUI did rename the file. But it gave me the output:
** (nautilus:11278): WARNING **: 22:11:35.868: Unable to get contents of the bookmarks file: Error opening file /root/.gtk-bookmarks: No such file or directory
And after I closed nautilus, it gave this output:
(nautilus:11278): Gtk-CRITICAL **: 22:12:25.397: gtk_widget_get_mapped: assertion 'GTK_IS_WIDGET (widget)' failed
(nautilus:11278): Gdk-CRITICAL **: 22:12:25.397: gdk_window_is_visible: assertion 'GDK_IS_WINDOW (window)' failed
(nautilus:11278): Gdk-CRITICAL **: 22:12:25.397: gdk_window_show_internal: assertion 'GDK_IS_WINDOW (window)' failed
(nautilus:11278): Gtk-CRITICAL **: 22:12:25.397: gtk_widget_set_opacity: assertion 'GTK_IS_WIDGET (widget)' failed
(nautilus:11278): Gtk-CRITICAL **: 22:12:25.397: gtk_widget_queue_draw: assertion 'GTK_IS_WIDGET (widget)' failed
(nautilus:11278): Gtk-CRITICAL **: 22:12:27.399: gtk_widget_get_mapped: assertion 'GTK_IS_WIDGET (widget)' failed
(nautilus:11278): Gdk-CRITICAL **: 22:12:27.399: gdk_window_is_visible: assertion 'GDK_IS_WINDOW (window)' failed
(nautilus:11278): Gtk-CRITICAL **: 22:12:27.399: gtk_widget_set_opacity: assertion 'GTK_IS_WIDGET (widget)' failed
(nautilus:11278): Gtk-CRITICAL **: 22:12:27.399: gtk_widget_queue_draw: assertion 'GTK_IS_WIDGET (widget)' failed
Best regards