Single Blog Layout

At the blog detail, you can check here and see the post detail with sidebar:

1. Add Post Widget on Single Blog Sidebar Layout

Admin -> Appearance -> Customize -> Widgets

Here you can drag n drop the available widgets such as Search, Blog category, Recent posts, Recent comments, Archives, Tags, ...

2. Customize Layouts for Single Post:

Customize > Blog > Archive

Sidebar position: Left/right sidebar

Select style: Default/Style 1/Style 2

Then "Publish" with all changes.