Hello Where_did_my_notes_go,
With the notes being synced by iCloud, you may try using the steps here to recover them via the iCloud site: 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 Notes 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.
If you happened to have removed any email accounts recently from the device then it's possible that the notes were linked to that account. In that case, you may try adding the account back to see if it has helped.
Cheers.
