Greasy Fork is available in English.
On pages which do not have a Table of Contents, but should do, create one! (I actually use this as a bookmarklet, so I can load it onto the current page only when I want it.)
< Σχολιασμός για τον κώδικα Table of Contents Everywhere
Suggestion: to make it draggable
It works well, looks good and dark mode add-ons make it black!