[BetterRed]

@gxn1 - restart in debug mode (there's an option in the Preferences drop down menu), then quit and wait, the log will display, copy it and post here - here's mine:

Spoiler:

ApplicationPaletteChange event ignored
Using calibre Qt style: True
ApplicationPaletteChange event received
calibre Debug log
calibre 8.16  embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.11.14
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
EXE path: C:\Program Files\Calibre2\calibre-debug.exe
Successfully initialized third party plugins: BRMenu Menu (1, 2, 0) && Backup Configuration Folder (1, 1, 2) && Calibre Config Reports (2, 0, 9) && Count Pages (1, 14, 4) && Drop Search Results (1, 0, 15) && Favourites Menu (1, 3, 1) && Find Duplicates (1, 10, 9) && Job Spy (1, 0, 239) && Modify ePub (1, 8, 8) && Scroll Book Details (1, 0, 2) && View Manager (1, 10, 3)
calibre 8.16  embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.11.14
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
EXE path: C:\Program Files\Calibre2\calibre-debug.exe
Successfully initialized third party plugins: BRMenu Menu (1, 2, 0) && Backup Configuration Folder (1, 1, 2) && Calibre Config Reports (2, 0, 9) && Count Pages (1, 14, 4) && Drop Search Results (1, 0, 15) && Favourites Menu (1, 3, 1) && Find Duplicates (1, 10, 9) && Job Spy (1, 0, 239) && Modify ePub (1, 8, 8) && Scroll Book Details (1, 0, 2) && View Manager (1, 10, 3)
QPA platform: windows
devicePixelRatio: 1.5
logicalDpi: 96.0 x 96.0
physicalDpi: 104.87741935483871 x 104.50285714285712
[0.00] Starting up...
[0.00] Initializing db...
[0.22] db initialized
[0.22] Constructing main UI...
[1.22] GUI main window shown
Job Spy has begun initialization...
orig_option = prefs.get[option_key]:  True
Tweak Library Name:  Books
'read_file_metadata' global.py file prefs.set  FROM:  True  TO:  True
'read_file_metadata' global prefs[option_key] value changed FROM:  True  TO:  True
author_sort_copy_method >>> default tweaks.py method is:  invert
current  tweaks['title_series_sorting']:  library_order
--->>>apply_title_series_sorting_by_library:   libname IS tweaked; new value for:  Books    is:  library_order
title_series_sorting changed FROM:  library_order  TO:  library_order
Calibre, and hence Job Spy, was gracefully shut down last time?  True
Last time daemon started:  never
Last time daemon failed:  never
Total daemon starts inception_to_date:  0
Total daemon failures inception-to-date:  0
Key 'Ctrl+Alt+A' for shortcut Discuss book with AI is already used by Show a menu of all available actions., ignoring
JS: ===>>> change_gui_alternating_row_colors()
Job Spy has finished initialization...
Key 'Ctrl+Alt+A' for shortcut Discuss book with AI is already used by Show a menu of all available actions., ignoring
Key 'Ctrl+Alt+A' for shortcut Discuss book with AI is already used by Show a menu of all available actions., ignoring
[1.66] main UI initialized...
[1.66] Started up in 1.66 seconds with 9 books
[22.44] Shutdown starting...
[22.73] [Backup Configuration Folder]: starting backup process
[24.09] [Backup Configuration Folder]: wrote config backup to C:\_AppData\Calibre\backup-Config_64bit\2025-12-06 -- 09-27-15.zip. Size: 15,491,103 bytes.
[24.11] [Backup Configuration Folder]: finished
[26.14] Shutdown complete, quitting...

As can be seen my shut down time is 3.7 seconds,


Aside: why do I get the messages about Ctrl+Alt+A?

As soon as I installed 8.16 I set the Discuss book with AI shortcut to None.

additional Environment variable CALIBRE_NO_NEW_DEFAULT_SHORTCUTS

BR