Ristretto not using libheif to open heic images?

[wakyct]

hello all, 

While trying to open a heic image with Ristretto (using xfce as my DE) I installed libheif. Now I can see heic thumbnails in 
Thunar, and use heif-convert from the terminal successfully, but Ristretto says "Unsupported mime type".

Any idea what the issue could be? Is there anyone using Ristretto that could check on their end for me? You can find sample 
heic files at https://filesamples.com/formats/heif.

It looks like libheif was linked correctly:

george@dunstan ~/.guix-profile/lib$ ls -l libheif*
lrwxrwxrwx 1 root root 70 Dec 31  1969 libheif -> 
/gnu/store/wvz8dzjnvgalhh74ayss6j0n1fn20ffy-libheif-1.17.6/lib/libheif
lrwxrwxrwx 1 root root 73 Dec 31  1969 libheif.so -> 
/gnu/store/wvz8dzjnvgalhh74ayss6j0n1fn20ffy-libheif-1.17.6/lib/libheif.so
lrwxrwxrwx 1 root root 75 Dec 31  1969 libheif.so.1 -> 
/gnu/store/wvz8dzjnvgalhh74ayss6j0n1fn20ffy-libheif-1.17.6/lib/libheif.so.1
lrwxrwxrwx 1 root root 80 Dec 31  1969 libheif.so.1.17.6 -> 
/gnu/store/wvz8dzjnvgalhh74ayss6j0n1fn20ffy-libheif-1.17.6/lib/libheif.so.1.17.6

AFAIK Ristretto should be able to work with libheif according to its doc page:

"The image types supported by Ristretto are those supported by the gdk-pixbuf library. This library itself supports a number of 
basic image types (JPEG, PNG, TIFF, etc.), but then relies on optional libraries to extend the range of supported image types. 
This means that you will have to install these libraries yourself to extend the range of image types supported by Ristretto. 
Examples: libwmf, libopenraw, libavif, libheif, libjxl, librsvg, webp-pixbuf-loader."


thanks, George