Whether the notes was encrypted before it was stored

[DoctorB]

I had the same question.
The answer is yes, the notes are encrypted locally on your workstation before being saved in the cloud.

The answer I received

Is everything you add to a Bitwarden vault encrypted?

You don’t have to rely on others to look into this for you. You can literally open the encrypted vault and look for yourself (see here for an example). The vault data file is called data.json, and its location is provided in the Bitwarden documentation.