theme advice sought

You’ll have to look through the themes yourself. The philosophy is that your content remains the same, but each theme can present that content with different styles. But themes don’t create content (such as footnotes), so they don’t really have a way to present them uniformly. Something like that would have to be either part of your content, or done by a plugin (so the theme isn’t involved and doesn’t matter).

But each page can have whatever arrangement of HTML that you care to enter. It isn’t up to the theme for that. The theme just provides the style of font and color and spacing and layout is only really about the bigger elements of header, content, sidebar, footer. (not link, image, text, footnote)

If the dropdown menu is something in your content, the theme is not involved and won’t help you. But if it is a navigation menu on every page, most themes provide that. You build the menu the way you want it in WordPress admin, and then choose where in your theme to display it.
As for sidebars, they are very useful for all users, and you don’t have to put that stuff in your page content. It is consistent across pages and changed in only one place (good for maintaining it easily). Most themes handle the sidebar for mobile devices by putting it at the bottom, or collapsing into the side edge. A site without sidebars is usually a bunch of pages that are dead ends. Sidebars give you a place to put more navigation or related information.

If you have WordPress installed already, you can go into the Customizer and preview how the different themes will look with your content. And each theme usually has options to change it at least a little (some have a LOT).