Add CPT product to main blog feed

I tried different codes in my function.php, but i’m still unable to make this work. I switched the plugin on and off, also inserted the register code directly into my functions.php and removed it from the CPT plugin.
I tried with another CPT that are still in the CPT plugin, nothing works.

I also added these two lines right after register_post_type( 'produkt', $args ); in my functions.php:

global $wp_query;
$query = $wp_query;

These are some of the codes I tried:

function my_cptui_add_post_types_to_rss( $query ) {
// We do not want unintended consequences.
if ( ! $query->is_feed() ) {
return;
}

// Replace these slugs with the post types you want to include.
$cptui_post_types = array('prod');

$query->set(
'post_type',
array_merge(
array( 'post' ),
$cptui_post_types
)
);
}
add_filter( 'pre_get_posts', 'my_cptui_add_post_types_to_rss' );

_________________________________-

function myfeed_request($qv) {
    if (isset($qv['feed']) && !isset($qv['post_type']))
        $qv['post_type'] = array('post', 'prod');
    return $qv;
}
add_filter('request', 'myfeed_request');

function prod_in_home_loop( $query ) {
if ( is_home() && $query->is_main_query() )
$query->set( 'post_type', array( 'post', 'prod') );
return $query;
}
add_filter( 'pre_get_posts', 'prod_in_home_loop' );

_______________________

What am I missing here?

Thanks! Caroline