New features
macOS: Various improvements to dark mode support
Viewer: Dont generate covers for books that dont have a cover. Note that because of this all previously opened books will again be prepared for first time reading.
Viewer: Restore print to PDF functionality
Viewer: Allow also jumping to book positions in Goto->Location
Content server: When adding books and a duplicate is suspected provide more information about what books match the duplicate
FB2 Output: Speed up conversion of images and handle external links
Viewer: If the book has no ToC try to generate one from headings, if any.
Closes tickets: 1847277
Viewer: Improve rendering of comics. No blank pages after large images or after every image in multi-page mode.
Viewer: Make it easier to use the bookmarks panel with only keyboard.
Closes tickets: 1847423
Viewer: Set the classes calibre-viewer-paginated and calibre-viewer-scrolling on the <body> tag in Paged and Flow modes. This allows the User styles to target these modes, if needed.
Closes tickets: 1847427
Viewer: Use the same loading spinner as is used by the rest of calibre
Bug fixes
Edit book: Fix a crash when editing CSS files caused by a behavior change in Qt 5.13.
Closes tickets: 1846760
Fix a regression in 4.0 that broke rendering of PDF covers for PDF files that used JPEG2000 compression.
Closes tickets: 1847567
Viewer: Fix a regression in 4.1 that broke creating new color schemes
Closes tickets: 1847407
Viewer: Fix error while viewing books with a comment after a <meta> tag.
Closes tickets: 1847977
Viewer: Fix an error when processing a CFI with an invalid text offset.
Closes tickets: 1848320
Viewer: Fix scrolling backwards to previous chapter not always scrolling to the end of the chapter, if the chapter loads external resources.
Closes tickets: 1847818
Viewer: Fix hang on books with namespaced attributes on <html> that do not belong to a known ebook namespace.
Closes tickets: 1846886
Viewer: Fix search history not persisting between viewer restarts.
Closes tickets: 1847976
Viewer: Fix scrollbar showing up on initial book open even if disabled in preferences.
Closes tickets: 1847323
Viewer: Fix rendering of books with mathematics failing
Viewer: When changing between individual sections/chapters in the book, only render the new chapter after loading is complete
Viewer: Fix scrolling by screenfuls not working correctly in flow mode
EPUB 2 metadata: Fix obfuscated fonts being broken when updating metadata if the file uses Adobe font obfuscation and the identifier with the key has an uppercase UUID scheme name.
Closes tickets: 1847890
Viewer: Fix right clicking on margins not showing controls
Viewer: Preselect text in search box when showing it.
Closes tickets: 1847677
Viewer: Fix SVG images that use xlink:href to refer to paths not being displayed.
Closes tickets: 1847181
Content server: Fix detection of iOS on iPAD with iOS 13 which defaults to desktop mode
Metadata jacket: Fix
tags in the comments not being rendered correctly when inserting the comments into the jacket page.
Closes tickets: 1848327
Viewer: Show nicer error message for DRMed books
Closes tickets: 1847468
Viewer: Fix preferences under Scrolling behavior not being saved correctly
Viewer: Fix remembered position sometimes off by one page in paged mode.
Closes tickets: 1847322
Viewer: restrict max size of margin page turn indicators to 25px rather than 75px
Viewer: Dont flash the home page before loading a book if a book has been specified
Viewer: Fix ctrl+m shortcut not working on windows
Content server: Fix regression that caused series name in book details view not not be blue to indicate it is clickable
Improved news sources
Various Polish news sources
Il Sole 24 Ore
http://calibre-ebook.com/