I'm very happy with this image viewer. It shows my HEIC image files nicely in full size unlike the other default image viewers which either couldn't display the HEIC image at all or displayed a thumbnail only. Of course I installed a bunch of libheif packages to support HEIC. But still, Viewnior was at least able to use those libheif libraries to render the images correctly.
The best minimalistic image viewer that isn't too minimalistic (ie. it has a GUI). Start-up is much faster than Mint's default image viewer, especially when using a slow hard drive, and switching from one image to antoher is quick.