Hello SKJ-,
Welcome to Apple Support Communities!
If we understand your post correctly, while setting up your new MacBook Air, one of your notes folders disappeared and you're unable to find it. We'd like to help!
"Notes is organized first by Quick Notes, then accounts (iCloud or On My Mac, for example), and then by folders. Some folders are automatically created. You can’t rename, delete, move, or share these folders.
- Quick Notes: Only appears if you create a Quick Note. See Start a Quick Note on Mac.
- All [account]: Only appears if you create your own folders. Shows notes from all folders in the account (except the Recently Deleted folder). For example, if you use iCloud notes, there’s an All iCloud folder. If available, it always appears first within the account.
- Notes: Contains notes that aren’t in folders you created or the Recently Deleted folder. The folder always appears second within the account.
- Recently Deleted: Only appears if you’ve deleted a note in the last 30 days. Recently Deleted shows notes that have been deleted from this Mac, from iCloud.com, or from your other devices. (Devices must be signed in to iCloud using the same Apple ID and have OS X 10.11 or later, iOS 9 or later, or iPadOS 13 or later.) This folder always appears last within an applicable account.
- Important: If you haven’t upgraded your iCloud notes or are using a notes account other than iCloud, there is no Recently Deleted folder, and deleted notes are removed permanently from all devices that use the same account."
For more information about folders in Notes, take a look at this article: About accounts and folders in Notes on Mac
Is your Mac the only place you're not seeing the folder?
Can you see the folder in any other Apple device?
Let us know if you have any questions.
Thank you for using Apple Support Communities.
Take care!