Step 1: write your book in LO. Use styling - italics and/or bold, etc. Use standardized styles.
SaveAs .docx
Step 2: use the
Sigil plug-in to import .docx into Sigil.
Step 3: use Sigil to clean up anything that needs it.
That’s it!
Definitely stay away from PDF. It makes an ugly mess and there is no need to use InDesign. That is predominantly/historically for printed books and it doesn’t do so well with epubs. You’d have more to cleanup once you got the file into Sigil.
edit: added plugin link