There are at least a couple of ways to have two post-displaying pages that contain nothing in common. These are:
1. Let both of them be category pages (see below). However, if one of them is to include all posts, and be a category page, rather than the blog page, then the category it represents would have to be assigned to each post. You could, for example, assign the category "blog" to every post.
2. Create two static pages and insert Display Posts Shortcode, customized to display posts assigned to one or more categories, into the page content of each.
See the Category Pages support page. There is only one blog page per WordPress.com site. You may use category pages to organize posts into separate groups. However, every post regardless of the category assigned to it will still appear in the blog page. I suggest that you do the following:
- Assign a category or multiple categories to posts corresponding to the category or categories you intend to include in the menu. See the Categories support page. A category page is automatically created when a category is added to at least one post. A specific category page grows each time you publish a new post with that category assigned to it, or assign that category to an old post.
- Include links to category pages among the main menu items of your custom menu. See the Additional menu items section of the Custom Menus support page. You may optionally nest links to the posts as sub-menu items beneath the category items, as described in the Changing the Order & Creating Sub-Menus section of the Custom Menus support page.