Can't enable password protection in Notes app
On one of my updates I didn't switched to the new Notes system, where you can draw and so on (because of incompatibilities). Now I want to switch:


Open Notes app.
Go back to folder
Tap the update button (on the top left, same height as iCloud)
Tap on update now
It takes some time and you see the number of notes he "converted"
Styling is differently. Now you can set your password.


Be careful when updating because there are some incompatibilities (MacBook must have OS X El Capitan, problems with multiple iCloud accounts on the same phone, ...). Don't know why Apple didn't make it work with both versions.