How to recover lost handwritten notes on iPad after Notes app crash?

Did you sync your notes to iCloud?

If yes, you might be able to recover them:

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You can recover and edit notes you deleted in the last 30 days on iCloud.com or on devices where you’re signed in to the same Apple Account. However, you can’t recover notes you permanently removed

1. Go to icloud.com/notes, then sign in to your Apple Account (if necessary).
2. Select Recently Deleted in the folder list.
3. If you’re on a phone or tablet and you don’t see the folder list, make sure the folder list is open.
4. If you don’t see Recently Deleted, you don’t have any notes in that folder, and there’s nothing to be recovered.
5. Select a note, then select Recover in the Notes toolbar.
6. The note moves to the Notes folder.
7. If you’re on a computer and 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.

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copied from: Delete and recover notes on iCloud.com - Apple Support

Also have a look at this article:

If you're missing notes on your iPhone, iPad, or iPod touch - Apple Support