Dear Maintainer,

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   * What exactly did you do (or not do) that was effective (or
     ineffective)?
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I use Debian (11.1), installed : Xfce (4.16), libgtk-3-dev (3.24) build-essential (10.2.1-6)

If i call :

Image_AchtungGefahrLinks = gtk_image_new ();
gtk_image_set_from_file (GTK_IMAGE (Image_AchtungGefahrLinks), "./__png's/achtunggefahrleer.png");
gtk_fixed_put (GTK_FIXED(AlteVersionWindowFixedLayout), Image_AchtungGefahrLinks, 15, 530-7+25);

I receive :

Gtk-WARNING **: 14:21:42.596: Could not load a pixbuf from /org/gtk/libgtk/icons/16x16/status/image-missing.png.
This may indicate that pixbuf loaders or the mime database could not be found.

**

Gtk:ERROR:../../../../gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /org/gtk/libgtk/icons/16x16/status/image-missing.png: Format der Bilddatei unbekannt (gdk-pixbuf-error-quark, 3)
Bail out! Gtk:ERROR:../../../../gtk/gtkiconhelper.c:494:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /org/gtk/libgtk/icons/16x16/status/image-missing.png: Format der Bilddatei unbekannt (gdk-pixbuf-error-quark, 3)
Aborted

if i call :

GError *error = NULL;
GdkPixbuf *pix = gdk_pixbuf_new_from_file ("./__png's/achtunggefahrleer.png", &error);
if (pix == NULL) {
    g_printerr ("Error loading file: #%d %s\n", error->code, error->message);
    g_error_free (error);
    exit (1);
}
GtkWidget *widget = gtk_image_new_from_pixbuf (pix);

I receive :

Error loading file: #3 Das Format der Bilddatei »./__png's/achtunggefahrleer.png« konnte nicht erkannt werden

the loaders are in
/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders

the loaders.cache is in
/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/

the png info in loaders.cache is
"/usr/lib/x86_64-linux-gnu/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-png.so"
"png" 5 "gdk-pixbuf" "PNG" "LGPL"
"image/png" ""
"png" ""
"\211PNG\r\n\032\n" "" 100

it seems that the pixbuf loaders can not be found

the image-missing.png is in

/usr/share/icons/Adwaita/16x16/status/ or /usr/share/icons/Tango/16x16/status/ or /usr/share/icons/gnome/16x16/status/ or /usr/share/man/man1/gtk+3.0-3.24.24/gtk/icons/16x16/status

but it searchs it in
/org/gtk/libgtk/icons/16x16/status