Make the account display name not a required field on My Account in WooCommerce on child sites.
Snippet Type
Execute on Child Sites
Snippet
add_filter('woocommerce_save_account_details_required_fields', 'wc_save_account_details_required_fields' );
function wc_save_account_details_required_fields( $required_fields ){
unset( $required_fields['account_display_name'] );
return $required_fields;
}