Change default file browser in Gnome (ubuntu 18.04)

install spacefm

Run (as regular user):

xdg-mime default spacefm.desktop inode/directory application/x-gnome-saved-search

As the shortcut for file-browsing was set to <super>+E - this shortcut launches SpaceFM

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to revert back:

xdg-mime default nautilus.desktop inode/directory application/x-gnome-saved-search