[davidfor]

With 5.99.5, I just got:

calibre, version 5.99.5
ERROR: Unhandled exception: <b>AttributeError</b>:'QStyleOptionViewItem' object has no attribute 'Alternate'

calibre 5.99.5*  embedded-python: True
Windows-10-10.0.19043 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19043')
Python 3.10.1
Windows: ('10', '10.0.19043', '', 'Multiprocessor Free')
Interface language: None
Successfully initialized third party plugins: Gather KFX-ZIP (from KFX Input) (1, 46, 0) && DeDRM (7, 2, 1) && Package KFX (from KFX Input) (1, 46, 0) && Annotations (1, 16, 0) && Calibre Power Search Plugin (2, 1, 1) && Clean Comments (0, 1, 0) && Clipboard Search (1, 3, 1) && Count Pages (1, 11, 2) && DOC Input (1, 0, 1) && Databazeknih (1, 4, 11) && Define Content (1, 0, 0) && Device Old Books (0, 0, 3) && Diaps Editing Toolbag (0, 3, 7) && Douban Books v2 (4, 2, 1) && Embed Comic Metadata (1, 6, 1) && EpubMerge (2, 12, 0) && EpubSplit (3, 2, 0) && Ex Libris (1, 0, 20) && Extract ISBN (1, 5, 0) && FanFicFare (4, 9, 0) && Fantastic Fiction (1, 5, 1) && Fantastic Fiction Adults (1, 2, 0) && Favourites Menu (1, 1, 0) && Find Duplicates (1, 9, 2) && Generate Cover (2, 1, 0) && GetFileName (0, 1, 1) && Goodreads (1, 5, 3) && Goodreads Sync (1, 15, 3) && Google Scholar (0, 1, 1) && Hyphenate This! (0, 1, 3) && Import List (1, 8, 1) && KFX metadata reader (from KFX Input) (1, 46, 0) && KFX Input (1, 46, 0) && Set KFX metadata (from KFX Output) (1, 58, 0) && KFX Output (1, 58, 0) && KePub Input (3, 4, 3) && KePub Metadata Reader (3, 4, 3) && KePub Metadata Writer (3, 4, 3) && KePub Output (3, 5, 3) && Kindle 2, 3, 4, Touch, PaperWhite, Voyage Device Interface MBP Update Mod (1, 0, 0) && Kindle hi-res covers (0, 5, 0) && Kobo Books (1, 8, 3) && Kobo Import (1, 0, 1) && Kobo Utilities (2, 15, 1) && KoboTouchExtended (3, 5, 4) && KoboTouchTOCUpdate (1, 2, 9) && LubimyCzytac (2, 2, 18) && METAmover (0, 0, 40) && Manage Series (1, 3, 0) && Manga (0, 1, 0) && Martinus.sk (2021, 12, 20) && Modify SOL Story (0, 10, 3) && Modify SOL Story (0, 10, 3) && Modify ePub (1, 7, 0) && Moly_hu (1, 1, 7) && Obok DeDRM (7, 2, 2) && Open With (1, 7, 0) && Overdrive Link (2, 50, 0) && Quality Check (1, 12, 0) && Quick Preferences (1, 5, 0) && Reading List (1, 8, 0) && Resize Cover (1, 1, 0) && ScrambleEbook (0, 4, 5) && Scroll Book Details (1, 0, 0) && Search The Internet (1, 8, 1) && Shentai (0, 0, 3) && Skoob Books (1, 5, 4) && SmartEject (2, 4, 0) && Smashwords Metadata (1, 0, 2) && Sort CSS (0, 2, 1) && Sum Column (0, 3, 1) && Unplugged (1, 0, 0) && User Category (1, 5, 5) && Velamma Comics (0, 0, 1) && View Manager (1, 7, 0) && Walk Search History (1, 3, 2) && Webscription (1, 1, 2) && WorldsWithoutEnd (0, 0, 2) && Overdrive Link* (2, 50, 0)
Traceback (most recent call last):
  File "E:\Development\GitHub\calibreQt6\calibre\src\calibre\gui2\tag_browser\view.py", line 124, in paint
  File "E:\Development\GitHub\calibreQt6\calibre\src\calibre\gui2\tag_browser\view.py", line 52, in draw_average_rating
AttributeError: 'QStyleOptionViewItem' object has no attribute 'Alternate'

That happened when trying to expand a letter under "Authors" in the tag browser. But, it seems to happen for any expansion. It only happens if both "Show average ratings" and "Use alternating row colors" are selected in the Tag browser settings.