change the class of Wall activity based on their privacy

//You can paste the following code in functions.php of your child-theme:

add_filter( 'bp_get_activity_css_class', 'bbwall_activity_css_class_privacy' );
function bbwall_activity_css_class_privacy( $classes='' ){
global $activities_template;
if ( function_exists( 'buddyboss_wall' ) && buddyboss_wall()->is_wall_privacy_enabled() ){
$classes .= ' privacy-' . bp_activity_get_meta( $activities_template->activity->id, 'bbwall-activity-privacy', true );
}
return $classes;
}