When trying to mount an SMB share using gio, you might encounter the following error:
$ gio mount smb://nas.corp.local
gio: smb://nas.corp.local/: Location is not mountable
This error might be due to a missing gvfs backend. The SMB backend should be located in /usr/share/gvfs/mounts/smb.mount. If it is missing, you should install the gvfs-backends package, and it should resolve the mounting issue.
If the mount was successful, but you can’t see it under $XDG_RUNTIME_DIR/gvfs/, you are probably missing the FUSE server that makes the mounted filesystem available to all applications, not only to GIO-aware applications. You can install the FUSE server by installing the gvfs-fuse package. The server will automatically run after reboot. If you want to start the server immediately, you can start it manually:
$ /usr/lib/gvfs/gvfsd-fuse /run/user/1000/gvfs