you could ask the murena.io helpdesk if they can restore individual note entries (files in “Notes/” at their end), though I’d imagine it’s a manual process for them. What do you see in your Notes/ folder btw? it’s what the Notes webapp looks at.
You can also retrieve the Notes app sqlite db if you can extract anything (Method 1 and 2). But if the changes back-propagated already there’s less chance. Notes app doesn’t keep in-db history really, it just isn’t robust.
I wonder how to reproduce Notes GenericEncryptionException. The user in your linked forum thread said it happened overnight. Here’s another user giving a bit of background.