Blog soll nicht nach Ende der ersten Kategorie die zweite Kategorie weiter gehen

there are different settings that can be done by that filter: avf_post_nav_settings
See: https://github.com/KriesiMedia/enfold-library/blob/master/actions%20and%20filters/Layout/avf_post_nav_settings.php

this is the common setting to get what you want in child-theme functions.php:

function enfold_customization_postnav($settings){
  $settings['skip_output'] = false;
  $settings['same_category'] = true;
  return $settings;
}
add_filter('avf_post_nav_settings','enfold_customization_postnav', 10, 1);

but you can have different settings for post or portfolio – you can exclude categories etc. pp
f.e.:

function enfold_customization_postnav($settings){
	$settings['skip_output'] = false;
	$settings['same_category'] = true;
	$settings['is_fullwidth'] = false;
	// exclude "category-id" 64 from post-navigation
	if('portfolio' == $settings['type']){ 
		$settings['excluded_terms'] = '64';
	}
	// posts will not have post-navigation
	if('post' == $settings['type'] ){ 
		$settings['skip_output'] = true;
	}
  return $settings;
}
add_filter('avf_post_nav_settings','enfold_customization_postnav', 10, 1);