Notes Disappeared!

In addition to the advice you already got: make sure that you are signed in to icloud. If not, the notes stored in your icloud account won't appear.

Do you have another device (iPhone, iPad or Mac)? You can check if the notes do appear in the other device, or login to icloud.com and check them there.

Hello swanflt,

Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with missing notes on your Mac. Try the steps listed here to see if you can recover them: Delete and recover notes on iCloud.com - Apple Support

"Recover recently deleted notes

You can recover and edit notes you deleted in the last 30 days on iCloud.com or on your devices that are signed in with the same Apple ID. However, you can’t recover notes you permanently removed.

1. In Notes on iCloud.com, select Recently Deleted in the folder list on the left.
2. If you don’t see Recently Deleted, you don’t have any notes in that folder, and there’s nothing to be recovered.
3. Select a note, then click Recover in the toolbar.
4. The note moves to the Notes folder.
5. If you want to move a recovered note directly to a folder you created, drag the note from the Recently Deleted folder to another folder.

Note: If you delete a shared note that you don’t own, the note doesn’t move to your Recently Deleted folder. See Delete shared notes on iCloud.com."

We hope this helps.

Cheers!