Is my data secure (encrypted)?

For syncing purposes, your data is stored on CloudKit (iCloud) and locally on your device (so you have offline access). Apple's iCloud servers use encryption to ensure that only authorized users can access data. We are not using an additional layer of encryption. The data is encrypted in transit by TLS (HTTPS).

As the developer, we have no access to your data. Your data can be accessed only with your private Apple ID login.

Additionally, to secure the locally saved data, you can enable "FileVault" in you system preferences:

You can enable an extra layer of encryption using "Save note as encrypted asset" in the Lab settings (only for App Store subscriptions).

This will store the contents of your notes as an "asset", which is by default encrypted by Apple on their servers. This includes the title of the note, but not the filename. Read more about this encryption method here.