Schema Extensions Manager is a SharePoint Framework (SPFx) solution (also Microsoft Teams / Microsoft 365 host ready) that provides a full UI to Create, Read, Update and Delete (CRUD) Microsoft Graph Schema Extensions and to track the extensions you have created in your tenant. It leverages Microsoft Graph (v1.0) /schemaExtensions endpoint together with SharePoint Tenant Properties (App Catalog site) to persist the list of schema extension IDs that were created through the tool so they can be rediscovered later.
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Source: https://github.com/pnp/sp-dev-fx-webparts/tree/main/samples/react-manage-schema-extensions