slow startup of calibre on macos 15.7.5

I've configured calibre 9.7 on MacOS Sequoia for the first time to hold my library of 428 books/journals (30 GB).
I wonder, why calibre takes more than a minute to startup. Even with a much smaller library, the startup time stays that long...

Here ist my debug output, which shows that a huge amount of time is taken during the "Constructing main UI..." phase:

macOS-15.7.5-arm64-arm-64bit-Mach-O Darwin ('64bit', 'Mach-O')
('Darwin', '24.6.0', 'Darwin Kernel Version 24.6.0: Fri Feb 27 19:34:42 PST 2026; root:xnu-11417.140.69.709.8~1/RELEASE_ARM64_T6020')
Python 3.14.2
OSX: ('15.7.5', ('', '', ''), 'arm64')
Interface language: de
EXE path: /Applications/calibre.app/Contents/MacOS/calibre-debug
QPA platform: cocoa
devicePixelRatio: 2.0
logicalDpi: 72.0 x 72.0
physicalDpi: 108.50000162950651 x 107.50000161448803
ApplicationPaletteChange event ignored
Using calibre Qt style: True
[0.00] Starting up...
[0.02] Showing splash screen...
[1.19] splash screen shown
[1.19] Initializing db...
[1.20] db initialized
[1.20] Constructing main UI...
[76.52] GUI main window shown
[76.56] main UI initialized...
[76.56] Hiding splash screen
[76.60] splash screen hidden
[76.60] Started up in 76.60 seconds with 428 books

Thanks for any ideas!