Hello kristieM7,
Thanks for reaching out to the Apple Support Communities. I understand you'd like to know if you can lock a shared note in the iOS Notes app to prevent your Christmas list information from being seen. This is a great idea. Currently you can either share a note or lock it. There's a great website where you can leave feedback and suggestions for what you'd like to be able to do: Feedback - iPhone - Apple.
While you cannot lock a shared note in the Notes app, you can set a password on a Pages, Numbers, or Keynote document that you and your husband can collaborate on. The apps are available on iOS, iPadOS, Mac, and on the iCloud website. You could access the document from any device. With the Collaborate feature, both you and your husband would have access to it. Adding a password ensures that no curious eyes can see the information in the document.
Here's the article: About collaboration for Pages, Numbers, and Keynote. I think you'll find these sections in the article helpful for what you want to do:
- Invite others to collaborate
- Set restrictions on documents
- Set a password
- Collaborate on a shared document
Cheers!