This was just discussed in the Editor forum here

:
https://www.mobileread.com/forums/showthread.php?t=239472
Specifically my answer here:
https://www.mobileread.com/forums/showthread.php?t=2831291
Sounds like you want the ncx Table of Contents, sometimes called the Active ToC -- it is semantic and ereaders will use it to create a navigation menu.
The builtin ToC Editor plugin can auto-generate these, but only as much as conversion would anyway. (You can also manually add entries and specify the location, but that is hardly "auto".

)
You need properly defined Chapter headings for it to work --see the linked explanation.
Good luck!