I use UnionTech OS, which is based on Debian. I downloaded the Debian version of "XnView MP 1.4.2" from https://www.xnview.com/en/xnviewmp/#downloads
I tried to install the package, but the installation could not be completed. Then, I downloaded XnView MP from the UnionTech repository, and the installation was completed successfully.

Now, whenever I double-click on an image file, XnView MP will be started, but the file will not be opened. I have to manually navigate to the containing folder on the left pane of XnView MP and then double-click on the file to open it.

How can I open a file simply by clicking without navigating?

When I run the above command, the .jpg file will be opened, so I have selected "xnview.sh" as the default program. However, I still cannot open the file with XnView simply by clicking. If I have selected other programs such as Image Viewer, Album, and Draw as the default program, the file can be opened simply by clicking.

I have no idea about the correct solution, but the usual way is to use something like this:
When you try to open an image file you can click on this XnView and set it as default viewer for jpg (and probably other type of images too).
you can edit the shortcut to contain the current filename, using a special notation - but it depends on your configuration. What kind of desktop do you use?

I went to the "Settings" of XnView and found no way to set it as the default viewer.

Deepin Desktop Environment.