How do I recover Notes deleted in error

Try looking in the Recently Deleted folder in the notes app. Recently deleted notes will appear in the recently deleted folder and will be stored there for 30 days and then will be permanently deleted.

You can also recover delete iCloud notes in iCloud.com.

Delete and recover notes on iCloud.com - Apple Support

Another way to recover deleted notes as long as the notes are on my iPhone Notes is to restore a backup that contains the notes. When you restore a backup, you overwrite the contains on your phone and replace it with the contents in the backup.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

You can restore your notes using the "Recently Deleted" option