Sequoia No Longer Supports QuickLook Generator Plug-ins
Prior to macOS 10.15 Catalina in 2019, the display of Thumbnails was supported by the QuickLook framework. From Catalina onwards, this is provided by a new framework named QuickLook Thumbnailing. The older framework is documented here, and had been deprecated for some years. Its replacement is documented here. To extend these, the older framework used QuickLook generators with the extension .qlgenerator, but in the newer framework this function is provided by QuickLook preview extensions, in particular Thumbnail Extensions, that were explained to developers at WWDC in 2019.
As with most deprecated features, eventually the time comes for Apple to remove support for the old, and for QuickLook generators that has occurred in macOS 15.0 Sequoia. From now on, QuickLook Generator plugins no longer work. Oddly, those provided by macOS in /System/Library/QuickLook are still named with the old extension of .qlgenerator, but all custom support now has to use the new framework in App Extensions.
These are controlled in the Quick Look item in Login Items & Extensions in General settings.
That should list all third-party app extensions providing this service, and enabling the right one(s) could fix some of those problems. But it turns out this list isn’t complete, and doesn’t in any case tell you which app extension handles which file type. For those, you’d normally turn to
qlmanage, but its-moption can only see the qlgenerators in macOS, and no third-party app extensions at all. In fact,qlmanageis now of little help for anything related to QuickLook.[…]
As far as I can discover, Apple doesn’t provide any equivalent of
qlmanagethat can report on QuickLook app extensions. The closest it comes is in thepluginkittool, that can list all app extensions known to macOS. With a bit of tweaking, its-moption can reveal which of those use the QuickLook SDKs for Thumbnails or Previews.
His Mints app makes it easier to view this information.
