I am using this to load JS like Mautic, Google Analytics, Facebook Pixel before redirecting to the target URL. This has only been tested a little but. Use at your own risk. It should still log the redirect but I have not checked that yet. In order for this to work you should create a page with the slug 'interstitial'. https://wordpress.org/plugi…

Interstitial JavaScript Redirect With WP Redirection by John Godley

add_action( 'redirection_url_target', 'wp_redirection_target');

function wp_redirection_target($url){

	if(!defined('THE_REDIRECTION_TARGET')){
 		define('THE_REDIRECTION_TARGET',$url);
 		return true;
 	}
}

add_action( 'wp_redirect', 'func_interstitial_redirect_get_url',1,1);

function func_interstitial_redirect_get_url($url) {
    
    if(!defined('THE_REDIRECTION_TARGET')){
			return $url;
		}

	        $add_js_content = '
				<script type="text/javascript">

				    window.setTimeout(function () {
				        window.location = "'.THE_REDIRECTION_TARGET.'";
				    }, 4000);
				</script>';
			


			add_filter( 'the_content', function( $content ) use ( $add_js_content ) {
			        return $content.$add_js_content;
			    }, 12
			);
			
			return false;

}


function func_interstitial_redirect() {

		if(!defined('THE_REDIRECTION_TARGET')){
			return;
		}
			
	        status_header( 200 );


	        $the_slug = 'interstitial';

	        $post = get_page_by_path($the_slug);

	        if(!empty($post->ID)){
			global $wp_query;
	        $wp_query->queried_object = $post;
	        $wp_query->is_single = true;
	        $wp_query->is_404 = false;
	        $wp_query->queried_object_id = $post->ID;
	        $wp_query->post_count = 1;
	        $wp_query->current_post=-1;

	     
			$wp_query->posts = array($post);
		}
}

add_action( 'template_redirect', 'func_interstitial_redirect');

FYI You can make that page look however you want in the wp admin and in the pages template file.