What is the purpose of All Devicer setting for Notification?
I think it's pretty self-explanatory - if the flag is set, it means that this notification applies to all devices.
If your geofence notification is not working, the most common mistake is not linking your geofences to devices.
Does it mean that I don't need to link notification to the device?
It would be good to have the same setting at geofence level.
Does it mean that I don't need to link notification to the device?
Correct.
It would be good to have the same setting at geofence level.
Geofence processing is expensive, so I don't think it's a very good idea. But if you want to automatically do it, you can link geofences to a group.
I have geofences and related notifications as on the screenshot.
Regardless of All Devices option notification is not sent.