If you got the qty box empty when you edit the product from the cart page, please follow the below instruction.

You need to override “vendor/magento/module-checkout/view/frontend/templates/cart/item/configure/updatecart.phtml” file in your theme

<vendername>/<themename>/Magento_Checkout/templates/cart/item/configure/updatecart.phtml

then just add below line in value

<?= $block->getProductDefaultQty() * 1 ?>

After making above changes QTY field code show will look like below:

<input type="number"
name="qty"
id="qty"
min="0"
value="<?= $block->getProductDefaultQty() * 1 ?>"
title="<?= $block->escapeHtmlAttr(__('Qty')) ?>"
class="input-text qty"
data-validate="<?= $block->escapeHtml(json_encode($block->getQuantityValidators())) ?>"/>

Note: I have tried this in Magento 2.3.6 – Let us know if it works with the other versions as well.