How to sort products by newest in Magento 2
By default, all products are sorted by Position in the category. On the category Edit page, you can manually re-order products for the particular category by adjusting the product's position.
Also using native Magento 2 functionality, you can sort products by attributes (important to mention, that you can use only user-defined attributes for sorting). To add a sorting option by attribute, you need to enable the option Used for Sorting in Product Listing on the attribute edit page.
Due to mentioned limitation, there is no way to sort products by the creation or updating date.
To get around that problem and sort products by newest (or update date) you can use Improved Sorting Magento 2 Extension.
The Improved Sorting extension implements sorting by the newest products and a few dozen other sorting options that are commonly must-haves for a modern e-commerce store.