GNOME Sushi doesn't work on Ubuntu 20.10, failing to preview anything. A workaround is available for those willing to put in the effort to get it working.
Ubuntu is considering adding the GNOME file preview utility Sushi as part of Ubuntu 17.10, the next stable release of the Linux distro due for release in October.
GNOME Sushi adds a macOS style 'Quick Look' feature to Nautilus. Just select a file and tap the spacebar to see a larger preview.