I think Notion has nailed it with the new design of their table of contents [1]. The problem with the current general approach is that if a blog post is very long and you are in the middle of it, you might forget what the content was. However, having a very small item on the right that you can quickly peek at is awesome.

[1] Example https://www.notion.so/notion/Table-of-contents-50de58f824bf4...