Calibre excels at converting books and maintaining a library. Its’ UX is subpar, and fixing that is effectively impossible because its maintainer (Kovid Goyal) is very cranky.
What I do is I set my preferred reader for EPUBs to Foliate and the preferred format to EPUB in Calibre and then convert the original copy that I have (usually KFX, AZW3, or MOBI) to EPUB. Then I whenever I select a book in Calibre it pops up Foliate instead of Calibre’s viewer.
