Use a filter for wp_robots to block CPT/feed/

We have a CPT (with base slug templates) that somehow included in every single post's head a link to /templates/post/feed/.

I've removed this link to the feed from the head, but want to block robots from the feed also.

From this answer, I can adapt code like:

add_filter( 'wp_robots', function( $robots ) {
  if ( is_singular( 'templates' ) ) {
    $robots['noindex']  = true;
    $robots['nofollow'] = true;
  }

  return $robots;
} );

but don't know how to include is_feed() into this code.

Would I use something like if ( is_singular( 'templates' ) is_feed( 'templates' ) ) ?

Help appreciated.

EDIT

Alternatively, I could somehow add the following to robots.txt:

User-agent: *
Disallow: /templates/*/feed

but do not know the function/hook to do this. We're using Yoast SEO.

Help appreciated.