Thumbnails for HEIF/HEIC files not showing

### What Happened?

When viewing a folder with heic files through the File app ( or Thunar File Manager ) thumbnails for the heic files do not show. A standard icon is displayed instead. It does appear that heif-gdk-pixbuf is installed and so is heif-thumbnailer.

There also is no default viewer for this file type. Installing Image viewer from the AppCenter allows me to view the files but the thumbnails still do not work.

### Steps to Reproduce

Open File manager to a directory with heif/heic files

### Expected Behavior

Thumbnail for the heif/heic file should be shown, not a standard icon.

### OS Version

7.x (Horus)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_