The solution proposed 4 years ago in this thread using ^[1]^ to create superscript does not work in 2023. It just adds ^[1]^ as additional text. One has to copy paste some text containing a superscript, and fiddle around with it when adding more footnotes ([2], etc.).
Not really something you would expect from a text editor.
Markdown is a solution that works, but unfortunately footnotes are not passed over multiple markdown cards. Making it impossible to insert other content and use markdown cards only for some nice features provided by markdown (tables, etc.).
In a world plagued with fake news, this feature is critical to make Ghost a publishing solution ready for serious journalism, or scientific articles.