I also downloaded the .DEB version of XnView, thinking I could build a VM that's Debian-based and run it from there. But I'd really like to display the pictures on our TV, so my wife and I could view them there. However, I don't really want to install VirtualBox on the media computer and create the VM there.
About all I can think of at this point is to install the .DEB file on a VM that I create on my laptop, and use its conversion ability to convert the .KQP files to a modern format that Linux can deal with on the media machine. This project is getting close to exceeding my interest in viewing these files.
And it's doing nothing to get me interested in AppImage files.