It looks like this will work until you create another note using the mobile client which is more up-to-date than your desktop client. When that note syncs to your desktop client it will not be able to read it.
Newer clients (Desktop version 2.11.11 and later) use AES256 to encrypt notes. The Play Store will automatically update your mobile client but you appear not to have done the same for your desktop client.
This post, which is currently pinned to the top of the forum, explains.