Handling mime types.

Custom file type associations can be found in .config/mimeapps.list.

mimeopen -d filename

Associate a file type to a default programm.

xdg-mime default nnn.desktop inode/directory

Set a different default file manager using a desktop file.f

To add a new mime type see the example for gemini.

To change the default user directories, edit ~/.config/user-dirs.dirs.