The proper way to do that is to use a CSS rule to replace the Overall background image with the new one on any page.
In the case of that page, if you remove your current image, you can make it the fixed background of that page using the rule below, added to the Theme Global Custom CSS Rule box
body.custom-background.page-id-4709 background-image: url(//no-stop.de/wp-content/uploads/2022/09/Workshops-im-Aftersales-Maschinenbau-20220908-scaled.jpg);background-attachment:fixed;background-size:cover;}