Date format cannot be changed anywhere

We use the child Max News and, as already described, cannot change the date format in all positions.

The english format is still used in the slide show and in the content area when listing the contributions.

We changed the system date in the WordPress settings.
How can we change it there in the places?

In the php files we could only find entries for the single page, which has an impact on the individual article.

The header date can be changed via the customizer, but the slideshow and the teased individual contributions are still on the start page.

The page I need help with: [log in to see the link]