Give Products extraordinary weight boost to ensure Products show up first.

searchwp-customizations.php

<?php

// Give Products extraordinary weight boost to ensure Products show up first.
// @link https://searchwp.com/documentation/knowledge-base/post-type-first-top/
add_filter( 'searchwp\query\mods', function( $mods ) {

  $post_type = 'product'; // Post type name.

  $source = \SearchWP\Utils::get_post_type_source_name( $post_type );

  $mod = new \SearchWP\Mod( $source );
  $mod->relevance( function( $runtime ) use ( $source ) {
    global $wpdb;

    return $wpdb->prepare(
        "IF( {$runtime->get_foreign_alias()}.source = %s, '999999999999', '0' )",
        $source
    );
  } );

  $mods[] = $mod;

  return $mods;
} );

I found that sometimes $mods is not an array, so to avoid fatal errors, I had to implement this at the start of the function:

if ( ! is_array( $mods ) ) {
	$mods = array( $mods );
}