Set default inventory/stock for new product

add_filter('wcfm_product_fields_stock', function ($fields, $product_id) {
    // For new product only
    if (!$product_id) {
        if (isset($fields['manage_stock'])) $fields['manage_stock']['dfvalue'] = 'enable';
        if (isset($fields['stock_qty'])) $fields['stock_qty']['value'] = '10';

        if ( WCFMu_Dependencies::wcfm_wc_appointments_active_check() ) {
            if ( current_user_can('manage_appointments') ) {
                if (isset($fields['_wc_appointment_qty'])) $fields['_wc_appointment_qty']['value'] = '10';
            }
        }
    }
    return $fields;
}, 91, 2);