You can show a sidebar on the blog home/archive and on single posts. They are 2 independent sidebars.
On Appearance → Customize → Blog → Blog Main enable the option Blog Sidebar. This will add the sidebar area for the Blog home page and archives only. The single articles sidebar is activated in Appearance → Customize → Blog → Single Post
After that add your widgets in Appearance → Widgets → Blog Sidebar
Single Post Sidebar
Activate the option Single Post Sidebar and select the sidebar position.
After that add your widgets in Appearance → Widgets → Article Sidebar