Install gnome-raw-thumbnailer by entering the following commands in the terminal:
sudo apt update sudo apt install gnome-raw-thumbnailer
Description:
RAW file thumbnailer for GNOME
gnome-raw-thumbnailer is a thumbnailer for GNOME that will make thumbnails for camera RAW files by extracting their preview. . http://gnome-raw-thumb.sourceforge.net/
Version: 2.0.1-0ubuntu9
Section: universe/graphics