Now that it is changed, everything is functioning to my liking, and I will make the following changes to the default ISO:
xdg-mime default mirage.desktop image/png...
xdg-mime default mirage.desktop image/jpeg
Here is a better way to implement this in VSIDO ISO,
Make the following directory structure in user's home directory
And create 'mimeapps.list' file there,
And in the 'mimeapps.list' file we can add associations and we can also set default applications.
Here is an example 'mimeapps.list' file,
We can add as many filetype associations we want and/or associate as many default applications as we want in the 'mimeapps.list' file.
I think this can be easily implemented via "/etc/skel" in VSIDO ISO.