Need to check whether the saveNewAddress function in the shipping.js is proper.
In my case, there was an error in JJ/Checkout/Plugin/Block/Layoutprocessor.php
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['firstname']['sortOrder'] = 1601;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['lastname']['sortOrder'] = 1602;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['city']['sortOrder'] = 1606;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['region_id']['sortOrder'] = 1607;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['postcode']['sortOrder'] = 1604;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['telephone']['sortOrder'] = 1603;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['street']['sortOrder'] = 1605;
$jsLayout['components']['checkout']['children']['steps']['children']['shipping-step']
['children']['shippingAddress']['children']['shipping-address-fieldset']
['children']['country_id']['sortOrder'] = 1608;
return $jsLayout; -> if this is missing we cannot add new shipping address in the checkout page.