You should be able to encrypt the folder where entries are stored with something like Veracrypt and have it prompt for a password when you turn your computer on.
Does this support markdown input or just text formatting via the pop-out box?
Having an issue with text rendering on Linux. Appears to work if the window is not resized after launch, but otherwise I have no text.
5.1.2-arch1-1-ARCH, i3wm, started from itch.io linux client.