This thread is for Sigil, but some good ideas will work in Calibre Editor and of course you can freely also install Sigil (best to Save Calibre file to Disk for Sigil and re-import via delete and add format in Calibre Metadata Editor View).
https://www.mobileread.com/forums/sh...d.php?t=355207
Not just applicable to invisible Chapter breaks or unnamed ones (like in Discworld or Dune).