Two different blog stylings for single blog posts?

you mean if you have category a it will be default – and if it is category b it is elegant ?

hm – if you style your blogs via the blog alb – means if you setup a page f.e. and show your blog with blog ALB – we can create a meta-box on the right side of your editor page:

put this into functions.php of your child-theme:

add_filter('avf_builder_boxes', 'register_global_blog_style', 10, 1);
function register_global_blog_style($boxes){
    $boxes[] = array( 'title' =>__('Layout','avia_framework' ), 'id'=>'layout', 'page'=>array('page' , 'post' , 'portfolio' ), 'context'=>'side', 'priority'=>'low');
return $boxes;
}

add_filter('avf_builder_elements', 'register_meta_blogstyle', 10, 1);
function register_meta_blogstyle($avf_builder_elements){
  $avf_builder_elements[] = array(
          "slug"  => "layout",
          "name"  => __("Blog Styling", 'avia_framework' ),
          "desc"  => __("Choose the blog styling here.", 'avia_framework' ),
          "id"  => "blog_global_style",
          "type"  => "select",
          "std"   => "",
          "no_first"=>true,
          "subtype" => array( 
                  __( 'Default (Business)', 'avia_framework' ) =>'',
                  __( 'Elegant', 'avia_framework' ) =>'elegant-blog',
                  __( 'Modern Business', 'avia_framework' ) =>'elegant-blog modern-blog',
                    ));

return $avf_builder_elements;
}

you will have than on the right in Layout Options the choice of setting blog_style for each page
see here : https://webers-testseite.de/blog-seite-elegant/
and: vice versa: https://webers-testseite.de/blog-seite-modern/

and again you can have here too f.e. the choice of header style for each page ;)

add_filter('avf_builder_boxes', 'register_meta_boxes', 10, 1);
function register_meta_boxes($boxes){
$boxes[] = array( 'title' =>__('Layout','avia_framework' ), 'id'=>'layout', 'page'=>array('page' , 'post' , 'portfolio' ), 'context'=>'side', 'priority'=>'low');
return $boxes;
}

add_filter('avf_builder_elements', 'register_meta_elements', 10, 1);
function register_meta_elements($avf_builder_elements){
$avf_builder_elements[] = array(
						"slug"	=> "layout",
						"name" 	=> __("Menu and Logo Position", 'avia_framework'),
						"desc" 	=> __("You can choose various different logo and main menu positions here", 'avia_framework'),
						"id" 	=> "header_layout",
						"type" 	=> "select",
						"std" 	=> "",
						"subtype" => array( __('Logo left, Menu right', 'avia_framework')  	=>'logo_left main_nav_header menu_right',
											__('Logo right, Menu Left', 'avia_framework')	 	=>'logo_right main_nav_header menu_left',
											__('Logo left, Menu below', 'avia_framework') 	=>'logo_left bottom_nav_header menu_left',
											__('Logo right, Menu below', 'avia_framework') 	=>'logo_right bottom_nav_header menu_center',
											__('Logo center, Menu below', 'avia_framework') 	=>'logo_center bottom_nav_header menu_right',
										));
$avf_builder_elements[] = array(
				          "slug"  => "layout",
				          "name"  => __("Blog Styling", 'avia_framework' ),
				          "desc"  => __("Choose the blog styling here.", 'avia_framework' ),
				          "id"  => "blog_global_style",
				          "type"  => "select",
				          "std"   => "",
				          "no_first"=>true,
				          "subtype" => array( 
				                  __( 'Default (Business)', 'avia_framework' ) =>'',
				                  __( 'Elegant', 'avia_framework' ) =>'elegant-blog',
				                  __( 'Modern Business', 'avia_framework' ) =>'elegant-blog modern-blog',
				                    ));

return $avf_builder_elements;
}

yes but it seems that there is something missing !
i started with Enfold Options Elegant – then it is possible to have modern because it only goes an additional class to html (html_modern-blog)
but from that point it does not remove the globaly set elegant if i choose business .
– i will try a different solution now – but had to remove those settings for now

sorry – it seems not to work propper

the thing is that on html there are the classes added – (html_blog-elegant, html_blog-modern) if they were present the blog will look this way we know. But adding it via addClass has a timeshift – thats ugly – so best would be to have a filter there similar to header-styling.