The Astra theme is like any other WordPress theme that lets you manage the global settings of the website. This includes colors, typography, layouts, headers, etc. The page content and design can be handled using the page builder or third-party plugins (like WooCommerce).
When a page is set to be the shop page, WooCommerce replaces it with an archive of products. It becomes a “post type archive” for the products in the store. That’s why it doesn’t act like a normal WordPress page.
One way some store owners handle this is to go on and assign a “placeholder” page to be the shop page. Then redirect this “placeholder” to the actual page you’ve designed.
This StackOverflow answer has a snippet you can use for this. You’d need to change it up just a bit to fit the page you’ve created, but hopefully, it’ll get you pointed to a solution. You can add the snippet to your theme’s functions.php file or with the Code Snippets plugin.