Thumbnails doesn't work for custom file type

Hi,


I tried to show thumbnails for my custom file type in a document based app. I already looked at the Particles example project and structured my app like this. But I still can't get the thumbnails work for my files. Breakpoints and logging also doesn't work for me in the extension.


What I've tried (using Xcode 11.4.1):

  1. Create a thumbnail extension
  2. Set the UTI in the Info.plist to the corresponding UTI that I used in the app
  3. Set the deployment target to iOS 13
  4. Link the QuickLookThumbnailing.framework to the extension and the app
  5. Run on a physical iPad and iPhone (although I don't want to support iPhones at the end)


But unfortunately nothing works. No matter what I try, the file in the document browser just shows the app's icon.

Please help me before I'm going crazy 😕