elpa-imenu-list binary package in Ubuntu Focal amd64

 This Emacs minor-mode creates an automatically updated buffer called
 `*Ilist*` that is populated with the current buffer's imenu entries.
 Imenu-list is usually configured so that the imenu structure is displayed
 in an automatically resized vertical Emacs window (a sidebar).
 .
 An imenu tree can be used as a table of contents for text and markdown
 documents, or for adding modern IDE features to Emacs--features like an
 overview of function and variable definitions. Speedbar also provides this
 functionality; however, imenu-list doesn't require X11. Unlike speedbar,
 imenu-list shares the existing Emacs frame. X11 windows are called frames
 in Emacs, so another way of saying this is imenu-list doesn't require a
 second X11 window with its own window decorations.

Source package