Created attachment 173959 [details]
Contains KritaUsageLog.txt, KritaSystemInformation.txt, Test.kra and screenshots of the aforementioned issue.

SUMMARY
Apple removed support for deprecated Quick Look Generator plugins (kritaquicklook.qlgenerator) from macOS 15 Sequoia, leading to empty thumbnails for .kra files and broken QuickLook previewing. Please migrate to Quick Look Preview Extension and Thumbnail Extension API. Documentation for developers can be found below.
Forum discussion: https://krita-artists.org/t/icon-thumbnails-not-displaying-on-mac-desktop/102375
macOS Sequoia 15 Release Notes: https://developer.apple.com/documentation/macos-release-notes/macos-15-release-notes#Quick-Look
Apple Developer Documentation Providing Thumbnails of Your Custom File Types: https://developer.apple.com/documentation/quicklookthumbnailing/providing-thumbnails-of-your-custom-file-types
Apple Developer Documentation QuickLook Thumbnailing: https://developer.apple.com/documentation/quicklookthumbnailing
Apple Developer Documentation QuickLookUI: https://developer.apple.com/documentation/QuickLookUI
Apple Developer Documentation QuickLook: https://developer.apple.com/documentation/quicklook

STEPS TO REPRODUCE
1. Install Krita via DMG or Homebrew on macOS 15 Sequoia.
2. Open Krita and save an image in .kra format.
3. Open Finder and find the newly saved .kra file.
OR
1. Upgrade from macOS 14 Sonoma to macOS 15 Sequoia with Krita and .kra files already on macOS 14 Sonoma.
2. Open Finder and find existing .kra files.

OBSERVED RESULT
Thumbnails are not displayed for .kra files. QuickLook preview does not work.

EXPECTED RESULT
Thumbnails should be displayed for .kra files. QuickLook preview should work.

SOFTWARE/OS VERSIONS
Windows: 
macOS: macOS 15.0 Sequoia
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION