Z-library was a massive pirate repository for ebooks.

Not sure if that was a typo but OP mentioned OnlyOffice, not OpenOffice. I don’t think OnlyOffice has ever tried to get me to make an account or do things on the cloud. I keep both Only and Libre installed. I like the UI of Only better, but Libre is more functional, at least as far as spreadsheets go which is my main use.