Do I Need to be Online to Edit my Notes?

No. Whenever your device is connected to the internet, OneNote synchronizes the local cache (a temporary copy of you open notebooks on your device) to the actual notebook files stored in the cloud (OneDrive or OneDrive for Business). While the device is offline, all changes are done to that cached local copy. This mechanism is the same for all OneNote versions.

Please consider this local “offline” cache versions of your notebooks not a backup copy or something you could transfer to another device bypassing the cloud. The cache is in a special binary format and not of any use by itself. Please also note that this cache is somewhat fragile. Resetting your mobile OneNote app or simply closing a notebook would erase it, thus deleting all changes since the last synchronization.

While it is possible to edit already opened notebooks offline, you can not create new notebooks or open ones that are saved in the cloud whithout and active internet connection. So it’s good practice to never close notebooks on your mobile devices to make sure you maintain access whuile being temporarily offline.