I don’t have personal experience with heif format images, however libheif has a list of software that uses their library
some notable examples
- gimp
- krita
- darktable
and several more. There is also a section for gnome desktop previews on that website, but you would probably have to create a nix package to make that work.
EDIT: sorry for xfce you might have to enable tumbler, libheif, and gdk-pixbuf and follow the other instructions on the site to get previews.