New features

Read aloud: Add the high quality Kokoro voices, which sound much more natural than the Piper voices, especially for English
To use them, select the Piper backend in the Read aloud configuration and choose one of the Kokoro voices. The voice will be automatically downloaded the first time it is used.

News download: Support for downloading news from websites that block automated access by using the camoufox browser
Some news sites, such as The New York Times, The Economist and The Atlantic, block all lighter weight ways of fetching their pages. Recipes for these sites now use the camoufox browser, which is automatically downloaded the first time such a recipe is run. Recipe authors can use it by setting browser_type = ‘camoufox’ in their recipes.

PDF Input: Support for right-to-left text and better handling of multi-column pages
Add support for reading images in the AVIF format
Tag browser: A new option to sort hierarchical tags that have only children but no actual books as folders, before all other tags at their level
Closes tickets: 2144044

Edit book: Check book: Allow skipping of problems of a particular type
Closes tickets: 2120771

Edit book: ToC View: Indicate what ToC entries, if any, are in the file being currently edited
Edit book: Check book: When auto fixing invalid ids also update CSS selectors
E-book viewer: Add an option to display the immediate parent ToC section in headers/footers
Closes tickets: 2169454

E-book viewer: Allow e-books to store up to 1MB of data persistently
Closes tickets: 2168471

E-book viewer: Print to PDF: Allow specifying margins in metric units
Closes tickets: 2148707

Tag mapper and HTML/CSS transform rules: Add the ability to search the rules
Closes tickets: 2150408

Allow removing individual entries from the search history dropdown
Closes tickets: 2167642

Add a button to Preferences->Look & feel->Main interface to reset the main window layout
Create your own Adventure: Allow exporting and importing saved games
Speed up various operations on large libraries, such as startup, deleting many books, sorting by series, searching and refreshing the Tag browser
Kobo driver: Add support for newer firmware
Closes tickets: 2168472

Windows: Unregister calibre from default programs and clear its caches when uninstalling
DOCX Output: Make images inside links clickable
Bug fixes

EPUB 3 to EPUB 3 conversions: Preserve ids on nav elements so links to them continue to work
Closes tickets: 2169441

PDF Output: Fix some trailing content at the end of individual HTML files being lost when the files use multi column layout
Closes tickets: 2142731

PDF Output: Fix a regression in 9.x that caused conversion of some books with vertical writing to not work correctly
Closes tickets: 2146979

DOCX Output: Fix non-breaking spaces not being preserved
Closes tickets: 2167710

FB2 metadata: Clear series, comments, etc. from the file when they are cleared in calibre
Closes tickets: 2168996

E-book viewer: Fix dark mode theme color overrides conflicting with e-book CSS when the book uses filters to change image colors in dark mode
E-book viewer: Update the “Pages from paper edition” value faster
Closes tickets: 2169232

E-book viewer: Fix an error when pressing ctrl+shift
Closes tickets: 2169575

Layout actions: Fix saving/restoring layout not restoring which of the alternate book list visualisations is currently active
Closes tickets: 2136805

Book list: Respect horizontal alignment setting for all icon only column types
Closes tickets: 2168620

Cover grid: Fix one cover being rendered too small in some circumstances
Content server: Various fixes for older browsers when using the book details page in the /mobile view
Content server: Various security hardening fixes
New news sources

World Socialist by Paulb223
Poetry Magazine by flurbs
The Believer by flurbs
Respekt by Vector Rilke
Improved news sources

The New York Times
The Economist (needs subscription)
The Atlantic
Reuters
Heise
La Jornada
Naked Capitalism
The Saturday Paper