pewc_get_products_for_cats_args.php

<?php
/**
 * Exclude specific products from a Product Categories field type
 * Edit the $excluded_ids array below with the product IDs you want
 * to hide. If you need different exclusions per field, check $args['category'] to
 * identify the field and apply exclusions conditionally.
 */
add_filter( 'pewc_get_products_for_cats_args', function( $args ) {

    // IDs of products to exclude from all Product Categories fields.
    $excluded_ids = array( 123, 456 );

    if ( ! empty( $args['exclude'] ) ) {
        $args['exclude'] = array_merge( $args['exclude'], $excluded_ids );
    } else {
        $args['exclude'] = $excluded_ids;
    }

    return $args;

} );