aside should not be used as a sidebar at all. Like the other answers, this is a semantic enhancement that is also named but not related to the sidebar / sidenav.
For a sidebar, using a div or section or nav (if it's a side navigation bar) would be more appropriate.
Think about the element aside, as your page speaks directly to the observer about the content in the same parent element. Use it to enhance or demonstrate the contents of this parent. Like a Shakespearean character talking to an audience. Good examples of aids are pullovers and pyrotechnics in print magazines.
However, for the sidebar, use a section or navigation and create it with css, floating to one side or the other.
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