Menu Bar in Posts?

Sure–just switch to a theme that does it that way. Whether the sidebar displays differently on certain parts of your blog than others is a decision that the theme designer made.

Thanks for advice Adam. Can you recommend a good source for themes?

https://themes.wordpress.net/

Or, in your exiting theme’s sidebar look for the conditional tags: if is_home… is_whatever
Those are excluding certain parts of the sidebar.