How to have all RSS feed entries linking to the same specific page

To have all RSS feed entries link to the same specific page, you can modify the permalink for each CPT entry before it is added to the feed.

One way to do this would be to use the post_link filter to modify the permalink for each CPT entry before it is added to the feed.

Here’s an example of how you could do this:

add_filter( 'post_link', 'wpm_custom_permalink', 10, 3 );
function wpm_custom_permalink( $permalink, $post, $leavename ) {
    if ( 'Evenements' === $post->post_type ) {
        // Modify the permalink to link to the desired page
        $permalink = 'https://website.de/de/aktivitaeten/';
    }
    return $permalink;
}

This code will modify the permalink for each CPT entry of type Evenements to link to the page

https://website.de/de/aktivitaeten/

Keep in mind that this will change the permalink for the CPT entries themselves, not just the links in the RSS feed. If you only want to modify the links in the RSS feed and not the actual permalinks for the CPT entries, you will need to use a different approach.

One possibility would be to use the the_permalink_rss filter to modify the links in the RSS feed without changing the actual permalinks for the CPT entries.