Exclude posts that have been displayed already by setting `avoid_duplicates` query var

avoid-duplicate-posts.php

// Based on code from https://ashton.codes/avoid-showing-wordpress-post-multiple-loops/

function sg_track_displayed_posts( $permalink, $post ) {
	global $sg_displayed_posts;
	$sg_displayed_posts[ $post->post_type ][] = get_the_ID();
	return $permalink;
}
add_filter( 'post_link', 'sg_track_displayed_posts', 10, 2 );
add_filter( 'post_type_link', 'sg_track_displayed_posts', 10, 2 );

function sg_remove_already_displayed_posts( $query ) {
	global $sg_displayed_posts;
	if (
		(bool) $query->get( 'avoid_duplicates' )
		&& isset( $sg_displayed_posts[ $query->get( 'post_type' ) ] )
	) {
		$query->set( 'post__not_in', $sg_displayed_posts[ $query->get( 'post_type' ) ] );
	}
}
add_action( 'pre_get_posts','sg_remove_already_displayed_posts' );