Editing an ebook (epub in my case, probably all types though) doesn't work, you get a pop up with an error message instead.
Seems to be this bug:
Corrected by this patch:
TLDR; PyQt incompatibility.
I just cp'd calibre-2.63.0.ebuild as calibre-2.66.0.ebuild in a local overlay and things are fixed.
Steps to Reproduce:
1. right on ebook, click edit
2. in the new window, on the left column, double click on a file to edit
3. look at the pop up error message with anger hoping it'll go away
no book editing
This is on ~amd64 installation with dev-python/PyQt5-5.7