I've been using Calibre on all my devices for years and have hundreds of books annotated.
Why would I switch to Foliate?
Not OP, I haven't used Foliate either.
Calibre UI is unappealing and too complex. Sometimes you just need a library of books without the clutter. Foliate looks simpler to use, but for some reason it doesn't allow bulk imports.
There is calibre-web[1] which some might prefer.