rewrite breadcrumb value

On my site i have a custom post type with a name: ‘cptposttype’ with a slug ‘Posttype’
The url looks good and shows up in the address bar like this:

The breadcrumb beneath the title on my posts shows the base cpt value: ‘cptposttype’, instead of the preffered slug ‘Posttype’:

I’ve found the following code in the knowledge base that i added as a code snippet. but there is no explanation how the $crumbs array is defined, which is why i can’t figure out how to re-write ‘cptposttype’ to ‘Posttype’
add_filter( 'rank_math/frontend/breadcrumb/items', function( $crumbs, $class ) {
return $crumbs;
}, 10, 2);