HEIC / HEIF images, such as most phone photos, now open with a built-in decoder, so you don’t need the Windows HEIC codec. The Windows (WIC) decoder is only used if the built-in one fails.
New document-type icons
Files associated with SumatraPDF use new icons for each document type (PDF, EPUB, comic books, CHM, DjVu, MOBI), and image files get their own icon instead of the PDF one (#5274).
Sticky note button in selection toolbar
The floating selection toolbar has a new Text button that adds a sticky-note annotation where the selection ends. The toolbar hides while you drag, and its setting is now called SelectionToolbar (was Annotations.SelectionToolbar).
Focus ring on the document
With the new ShowDocumentFocusIndicator advanced setting (off by default), a focus ring is drawn around the document when it has keyboard focus (#4644).