Lightning Experience app. It’s a paid product. Used for masking data and provide Data Security.

Anonymization – Replacing with Random Characters.
Pseudonymization – Replacing from Library.

Below should be enabled in the org
1. MyDomain
2. Lightning Experience
3. Enhanced Email

Troubleshooting:
1. Delete option is not available for required fields.
2. For Person Account, select Name, First Name and Last Name fields for masking.
3. Don’t select Delete Chatter if the chatter is not enabled in the org.