App Check helps protect your API resources from abuse by preventing unauthorized clients from accessing your backend resources. It works with both Firebase services, Google Cloud services, and your own APIs to keep your resources safe.
Please follow the following link to configure AppCheck: https://firebase.google.com/docs/app-check
This feature is updated in Integrate Firebase PRO v3.17.0. All you need to do is to enter the reCaptcha Site (public) Key to the WordPress Dashboard > Firebase > General.
Configure AppCheck