Printing in US Letter size instead of A4 - Printer error

Comienza reproduciendo el problema mediante el flujo de la página de prueba del servidor web de Ghostscript con la configuración indicada de las impresoras CUPS, Raspberry Pi y Dell. Compara la configuración de medios y márgenes enviada con la configuración A4; se considera completado cuando el trabajo conserva A4, mantiene los márgenes y finaliza sin el error de la impresora.

When I print, I always get the printer output set back to "Letter" size. Correct size would be A4. Then the print job stops with an error code, and I need to unlock the printer manually by erasing the print job.

Setup:

Ghostscript Version 10.03.0-3 installed through Snap on a Raspberry Pi4B/4GB, running RaspianOS Bookworm. All updated.
CUPS 2.4.2 installed on the Raspi.
Dell 1355cnw printer as network printer installed

Printer settings in CUPS:
Beschreibung: Dell_MuFu
Ort: HomeOffice
Treiber: Dell 1355 Foomatic/foo2hbpl2 (recommended), driverless, cups-filters 1.28.17 (farbig, 2-seitiges Drucken)
Verbindung: implicitclass://Dell_MuFu/
Standardeinstellungen: job-sheets=none, none media=iso_a4_210x297mm sides=one-sided

Printer settings in Ghostscript:
Medien: A4 ( Plain ) Medien konfigurieren
Orientierung: Portrait Landscape Reverse Landscape Reverse Portrait Auto
Druckmodus: Automatisch Farbe Monochrom
Druckqualität: Draft Normal High
Optimieren für:
Skalierung:
Druckauflösung: 300 dpi
printing-quality:
color-mode:
halftone-algorithm:
icm-color-profile:
n-up-orientation:
n-up-printing:

Printer Tray settings:
MPF Paper Type | Plain
MPF Paper Size | A4 (210 x 297 mm)
MPF Custom Size - Y | 297 millimeters
MPF Custom Size - X | 210 millimeters
Display Popup | On

This are the start settings. Whenever I print (paper size set to A4 in the print dialogue of the app), the printer claims it has "Letter" instead of A4 paper format.

Furthermore the Tray settings of the printer are set back to "Letter". The printer is not touched by anything, beside the print job being send to the printer.

This happens no matter if printing through AirPrint from an iPhone, or by Ethernet from a Mac (both on the current OS versions). But it already happens when I send a test page from the Ghostscript web server site.

In addition the margins of the page are set to zero: It starts printing right on top of the page, and has no left margin.

I have no idea why the settings are changed to US Letter size by itself - I am located in Germany and never use US letter.

Picture of Test page