To switch your layout for an archive or single post, navigate to Appearance -> Editor. From the sidebar click Templates then select Single.
Click on the plus icon in the top left corner and switch to the Blocks tab. Scroll down to find the Single Layout 3 With Sidebar template part and click on it to add it to your page.
Open the List view (Shift+Alt+O) and you’ll now see two template parts. You can now delete the old Single template part and save the changes. This will enable a single post layout with sidebar on all the single posts.
