I was merely giving you an example of what could cause Touch ID to no longer work.
There is likely a short list of things that could cause this.
As I stated previously, unless you specifically saved your Notes password to Keychain, it would not be there.
Keychain tends to work best for websites with a username and password.
Also as I stated, just because you were using Touch ID does not mean you can forget the password. Using Touch ID is a convenience to make it quicker and easier for you to access your locked Notes.
You should never rely on Touch ID.
Similarly:
If you rely on Touch ID and forget the passcode to your iPhone, you stand to lose all the data on your phone (unless you have a backup, are you backing up your device btw?).
How is this any different?
Microsoft has nothing to do with these locked notes.. I assume you meant Apple.
I would not call this a blunder at all. It's misunderstanding and security.
Misunderstanding: You thought that Touch ID replaced your password and it does not.
Security: The password is unknown, now you will not be able to access your Note
Sorry, I know this isn't what you want to hear.
Use the link in my first post to reset your password.
When you create the new password, include a password hint if you want one.
Once you have your new password set, if you want it saved in Keychain..
go to Settings > Passwords, tap the + in the upper right
Here you can enter whatever you want. Although the website field has to resemble a web address.
I tested adding and put in the info below and it worked fine.
I had to put .com after Notes or it wouldn't allow me to save it.
website: Notes.com
username: me
password: [whatever your password is]