how to make order summary field unfolded on Mobile?

Hello @cheonmu!

Thanks for reaching out!

And on mobile, the order summary field on the checkout page is collapsed.

screenshot -> https://imgsh.net/a/vU6L6jD.png

I want to make this always unfold.

Could you please tell me what should i do?

The collapsed order summary feature for mobile devices when using the Checkout Block from WooCommerce Blocks is controlled through JavaScript scripts as laid out in the GitHub request here: https://github.com/woocommerce/woocommerce-blocks/issues/2423

There is no built-in way to disable that feature without customization work, which falls outside the scope of support for this forum.

You can, however, consult our experts for customization work here: WooCommerce Customizations Page.

Please note that the Cart and Checkout Blocks are still in active development and you can submit a feature request for the scenario you described here: https://woocommerce.com/feature-requests/woocommerce-gutenberg-products-block/

Hope this helps!