Prefetch a list of URLs

By prefetched do you mean “precached“?

Yes, sorry, there is the rel=prefetch thing I was looking into, so I posted that way.

You can see documentation for this in the wiki under Route Caching API. In particular, here’s how you would precache an image:

<?php
add_action( 'wp_front_service_worker', function( \WP_Service_Worker_Scripts $scripts ) {
	$scripts->precaching_routes()->register(
		'https://example.com/wp-content/themes/my-theme/my-theme-image.png',
		array(
			'revision' => get_bloginfo( 'version' ),
		)
	);
} );

You can duplicate that register call as, any times as you need.