[DNSB]

I would also suggest running calibre from a CLI using calibre-debug -g and see what if any error messages are reported during startup. I've attached a truncated example of what I see on a normal startup for calibre using my Intake library.

Spoiler:

Microsoft Windows [Version 10.0.26200.7705]
(c) Microsoft Corporation. All rights reserved.

C:\Users\<user>>calibre-debug -g
calibre 9.0*  embedded-python: True
Windows-11-10.0.26200-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '11', '10.0.26200')
Python 3.14.2
Windows: ('11', '10.0.26200', 'SP0', 'Multiprocessor Free')
Interface language: None
EXE path: C:\Program Files\Calibre2\calibre-debug.exe
Successfully initialized third party plugins: ACSM Input (0, 1, 0) && LCPL Input (0, 0, 5) && Gather KFX-ZIP (from KFX Input) (2, 28, 0) && DeDRM (10, 0, 15) && AZW6 Image Merge (1, 1, 2) && Package KFX (from KFX Input) (2, 28, 0) && ACSM Input Plugin GUI Extension (0, 1, 0) && Apple Books covers (1, 1, 0) && Backup Configuration Folder (1, 1, 2) && Baen (1, 1, 0) && Barnes & Noble (1, 5, 7) && Count Pages (1, 14, 4) && Diaps Editing Toolbag (0, 5, 0) && EpubCheck (0, 2, 6) && EpubMerge (3, 2, 0) && EpubSplit (3, 12, 0) && FanFicFare (4, 53, 0) && Find Duplicates (1, 10, 9) && Generate Cover (2, 3, 6) && Goodreads (1, 8, 3) && Job Spy (1, 0, 239) && KFX metadata reader (from KFX Input) (2, 28, 0) && From KFX (2, 28, 0) && KFX Input (2, 28, 0) && Set KFX metadata (from KFX Output) (2, 18, 0) && KFX Output (2, 18, 0) && Kindle hi-res covers (0, 5, 1) && KindleUnpack - The Plugin (0, 83, 8) && Kobo Metadata (1, 12, 0) && Kobo Utilities (2, 25, 0) && Modify ePub (1, 8, 8) && Obok DeDRM (10, 0, 9) && Open With (1, 8, 4) && OverDrive Libby (0, 2, 101) && Quality Check (1, 14, 6) && Resize Cover (1, 2, 1) && ScrambleEbook (0, 6, 0) && SmartEject (2, 6, 0) && Smashwords Metadata (1, 0, 2)
QPA platform: windows
devicePixelRatio: 1.0
logicalDpi: 96.0 x 96.0
physicalDpi: 81.55183946488295 x 81.64285714285714
ApplicationPaletteChange event ignored
Using calibre Qt style: True
ApplicationPaletteChange event received
[0.00] Starting up...
[0.00] Showing splash screen...
[1.14] splash screen shown
[1.14] Initializing db...
[1.17] db initialized
[1.17] Constructing main UI...

<much removed to shorten the log segment>

Driver: KoboTouch'
[2.53] main UI initialized...
[2.53] Hiding splash screen
[2.53] splash screen hidden
[2.53] Started up in 3.53 seconds with 17 books