My first assumption was, that there was somewhere in the wordpress file hierarchy set the wrong link. So I searched all wordpress files for the appearance of the link programmiereninpython.org. I found three files that have that link listed:
./wp-content/uploads/uag-plugin/assets/0/uag-css-100.css
./wp-content/uploads/uag-plugin/assets/0/uag-css-323.css
./wp-content/uploads/uag-plugin/assets/0/uag-css-77.css
But all three files only contain pictures that were uploaded to the side, like this line of code shows:
background-image: url(https://programmiereninpython.org/wp-content/uploads/2022/10/Call-to-action.jpeg)
I am clueless how this could happen.