Hello,
We have disabled the Emil builder and made test order. We got a new order email https://prnt.sc/NyFk4Htd2Vyl . Then we changed the status of the order to on-hold and there is no on-hold email even if the email builder is disabled https://prnt.sc/o3BUdHcrh7iJ So, email builder is not the reason of the issue. Provide us with the video of your order with the enabled Storefront theme and on-hold email that you get when the Storefront theme is enabled. Because I think that you won’t get the email even with the Storefront and that you need to contact WooCommerce support about this.
Regards