Notes - Quick/Notes

Not sure what you just said but, to open the Sidebar, hover the cursor over the left edge of the Notes window until it changes to a horizontal direction cursor. Then click and drag to the right until the Sidebar opens.

Just to add in case, a Quick Note window has no sidebar. Only the Notes app has one.

The first thing you need to do is open the Notes window. Either from the Window menu or by pressing command+o.

edit: sorry, the Window menu not the View menu. ::smh::

You're welcome.