In Ubuntu 18.04 I installed a program called FSLeyes and would like this program to become associated with files containing the '.nii.gz' extension. I have created a '.desktop' file for the application, which I placed in the /usr/share/applications folder, and I can now find the application from the Activities menu and run it without problems. However, when I right-click a '.nii.gz' file and go 'properties->open with' or 'open with other application' the installed program (fsleyes) is not in the list of available applications. Why not?
Linking the application to /usr/bin
sudo ln -s /usr/share/fsl/5.0/bin/FSLeyes /usr/bin/FSLeyes
does not solve the problem either.