Hi,
I would like to suggest a new feature to Joplin. I often use many header levels in a note. With a small note, I can easily manage how is it going. But with the bigger one, I hope I can see all the main content of the note based on headers. So, please consider it.
I attached a screenshot from MS Word. I hope you can understand what it is.

Have you tried the TOC for markdown?
https://joplinapp.org/markdown/#plugins
Or the Outline Plugin?
Oh. That's great. Thanks for your reply. The Outline plugin looks good for me.