Hiya,
The information about whether an application has an IdP configured for it is stored on the identity provider object, not on the application.
So the easiest way to answer your question is to retrieve all the identity providers (or one, if you have a target), then filter through the JSON looking for your application id.
https://fusionauth.io/docs/v1/tech/apis/identity-providers/#retrieve-all-identity-providers shows how to list all Identity Providers.
If you look at the results, you'll see a field similar to:
"applicationConfiguration": { "1c212e59-0d0e-6b1a-ad48-f4f92793be32": { "createRegistration": true, "enabled": true } },for each of the identity providers.
The applicationConfiguration has keys, each of which is an application Id.
Does that help?