note

If you deleted part of the text and didn’t try to use the undo feature on the keyboard at the time. The text has been deleted for good from the device.

If you include notes in your backups, and this complete unedited note is in the backup, you could restore the backup, but when you do that you restore everything in the backup and the current data in your device is overwritten.

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

If you are using Notes with iCloud, the text is not retrievable now.

The Undo key is on the keyboard to the right of the space bar and it is where the .?123 key is. If you tap on the .?123 key, this is what you see.

It can only be used right away when you type something. It allows you to recover the last words, phrase or sentence that you typed. It would too late for you to invoke it now for any purpose and it wouldn’t work to recover the folder of notes.

If you deleted a folder of notes on iCloud.com, take a look at this for help.

Delete and recover notes on iCloud.com - Apple Support

I mistakenly deleted a large folder on notes located on iCloud. Have no idea I even have an undo button. Please, please, please help me retrieve it.