Filter products from a specific custom meta data in Woocommerce shop page

You can use a custom function hooked in woocommerce_product_query_meta_query filter hook, where you will replace _the_meta_key in the code below, by your targeted meta_key:

add_filter( 'woocommerce_product_query_meta_query', 'show_only_products_with_specific_metakey', 10, 2 );function show_only_products_with_specific_metakey( $meta_query, $query ) {    // Only on shop pages    if( ! is_shop() ) return $meta_query;    $meta_query[] = array(        'key'     => '_the_meta_key',        'compare' => 'EXISTS'    );    return $meta_query;}

Code goes in function.php file of your active child theme (or active theme). Tested and work.

Addition (related to your last comment):

To make it work for multiple meta values you need to use 'compare' => 'IN', like:

add_filter( 'woocommerce_product_query_meta_query', 'show_only_products_with_specific_metakey', 10, 2 );function show_only_products_with_specific_metakey( $meta_query, $query ) {    // Only on shop pages    if( ! is_shop() ) return $meta_query;    $meta_query[] = array(        'key'     => '_the_meta_key',        'value'     => array('L','XL'),        'compare' => 'IN'    );    return $meta_query;}

Code goes in function.php file of your active child theme (or active theme). Tested and work.

WP meta_query documentation

you can use do_action( 'woocommerce_shop_loop' );

function ctm_loop_53631963(){    global $post;    $meta = get_post_meta($post->ID, 'meta_value_key')    if($meta !== 'desired_value'){        continue;    }}do_action('woocommerce_shop_loop', 'ctm_loop_53631963');

read more about wordpress actions Plugin API/Action Reference